Commit Graph

468 Commits

Author SHA1 Message Date
Xiang W
cc89fa7b54 lib: sbi: Fix printc
Because *out needs to reserve a byte to hold '\0', no more characters
should be added to the buffer when *out has one byte left, and the
buffer size *out_len should not be modified. this patch prevents
the correction of *out_len when *out_len is 1.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 10:02:27 +05:30
Xiang W
3b6fcddceb lib: sbi: Simplify prints
When doing width = width - strlen(string) in prints there is no need
to consider the case that witdh may be less than 0. This is because
the code to do filling needs to be executed under the condition that
width > 0.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 10:02:06 +05:30
Xiang W
c6ee5ae5a4 lib: sbi: Fix printi
Fix two bug:
> printf("%#08x", 0x123); /* print 0000x123 */
> printf("%#x", 0); /* print 0x0 */

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 10:01:43 +05:30
Xiang W
fe0828142f lib: sbi: print add 'o' type
Add o type for print to print octal numbers

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 09:59:22 +05:30
Xiang W
05cbb6e908 lib: sbi: implifying the parameters of printi
The information of sg/b/letbase can be obtained by the type character,
simplifying the parameter by passing the type directly.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 09:58:52 +05:30
Xiang W
458fa74266 lib: sbi: Add ' ' '\'' flags for print
The space flag is used to add a space before positive numbers, and
apostrophe is used to print the thousand separator. Add code to
ignore these two flags

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 09:58:00 +05:30
Xiang W
40dac06e3c lib: sbi: Add '+' flags for print
Adds + flags for print, prefixing positive numbers with + when this
flags is present

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 09:57:48 +05:30
Xiang W
35ef182690 lib: sbi: print not fill '0' when left-aligned
Left alignment and padding '0' should not exist at the same time,
this patch skips padding.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 09:48:49 +05:30
Xiang W
6053917626 lib: sbi: Fix how print gets flags
The flags for print should be able to appear in any order. The
previous code required the order to be fixed.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-12 09:39:38 +05:30
Ley Foon Tan
976895c57e lib: sbi: Fix Priv spec version for [m|s]counteren and mcountinhibit CSRs
Fix Priv spec version typo in commit d4b563c881 ("lib: sbi: Remove MCOUNTEREN
and SCOUNTEREN hart features").

At least Priv spec v1.11 is required for [m|s]counteren and mcountinhibit CSRs.

Fixes: d4b563c881 ("lib: sbi: Remove MCOUNTEREN and SCOUNTEREN hart features")
Signed-off-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-09 11:08:35 +05:30
Anup Patel
5359fc6955 lib: sbi: Rename hart_pmu_get_allowed_bits() function
The hart_pmu_get_allowed_bits() function detects implemented bits
of mhpm counters so let us rename this function accordingly.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
2023-07-09 11:06:30 +05:30
Anup Patel
72b9c8ff89 lib: sbi: Alphabetically sort HART ISA extensions
Let us follow alphabetical order for HART ISA extension so that
it is simpler to maintain.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
2023-07-09 11:06:28 +05:30
Anup Patel
669089c5f2 lib: sbi: Add Zihpm as a HART ISA extension
Recently ratified Zihpm ISA extension covers all [m]hpm* CSRs
so we add Zihpm as a HART ISA extension in OpenSBI.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
2023-07-09 11:06:26 +05:30
Anup Patel
1a398d9faa lib: sbi: Add Zicntr as a HART ISA extension
Recently ratified Zicntr ISA extension covers cycle, time and
instret CSRs so we replace the "time" ISA extension with "zicntr"
ISA extension in OpenSBI.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
2023-07-09 11:06:24 +05:30
Heinrich Schuchardt
eb736a5118 lib: sbi_pmu: Avoid out of bounds access
On a misconfigured system we could access phs->active_events[] out of
bounds. Check that num_hw_ctrs is less or equal SBI_PMU_HW_CTR_MAX.

Addresses-Coverity-ID: 1566113 ("Out-of-bounds read")
Addresses-Coverity-ID: 1566114 ("Out-of-bounds write")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-05 09:29:24 +05:30
Gianluca Guida
0907de38db lib: sbi: fix comment indent
Use tabs rather than spaces.

Signed-off-by: Gianluca Guida <gianluca@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-07-05 09:25:32 +05:30
Gianluca Guida
8bd666a25b lib: sbi: check A2 register in ecall_dbcn_handler.
Do not ignore register A2 (high bits of physical address) in the dbcn
handler (RV64).

Signed-off-by: Gianluca Guida <gianluca@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-06-23 08:46:07 +05:30
Anup Patel
66daafe3ba lib: sbi: Use scratch space to save per-HART domain pointer
Instead of using a global array indexed by hartid, we should use
scratch space to save per-HART domain pointer.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
2023-06-05 15:55:21 +05:30
Anup Patel
ef4542dc13 lib: sbi: Use heap for root domain creation
Let's use heap allocation in root domain creation instead of using
a fixed size global array.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
2023-06-05 15:50:33 +05:30
Anup Patel
bbff53fe3b lib: sbi_pmu: Use heap for per-HART PMU state
Instead of using a global array for per-HART PMU state, we should
use heap to on-demand allocate per-HART PMU state when the HART
is initialized in cold boot or warm boot path.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
2023-06-05 15:48:43 +05:30
Anup Patel
2a04f70373 lib: sbi: Print scratch size and usage at boot time
The scratch space being a scarce resource so let us print it's
size and usage at boot time.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
2023-06-05 15:46:22 +05:30
Anup Patel
40d36a6673 lib: sbi: Introduce simple heap allocator
We provide simple heap allocator to manage the heap space provided
by OpenSBI firmware and platform.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
2023-06-05 15:46:09 +05:30
Andrew Jones
bdde2ecd27 lib: sbi: Align system suspend errors with spec
The spec says sbi_system_suspend() will return SBI_ERR_INVALID_PARAM
when "sleep_type is reserved or is platform-specific and unimplemented"
and SBI_ERR_NOT_SUPPORTED when sleep_type "is not reserved and is
implemented, but the platform does not support it due to one or more
missing dependencies." Ensure SBI_ERR_INVALID_PARAM is returned for
reserved sleep types and that the system suspend driver can choose
which of the two error types to return itself by returning an error
from its check function rather than a boolean.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-06-04 15:18:40 +05:30
Xiang W
8b99a7f7d8 lib: sbi: Fix return of sbi_console_init
console is not a required peripheral. So it should return success when
the console does not exist.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-26 12:36:54 +05:30
Andrew Jones
c3e31cbf36 lib: sbi: Remove 0/1 probe implementations
When a probe implementation just returns zero for not available and
one for available then we don't need it, as the extension won't be
registered at all if it would return zero and the Base extension
probe function will already set out_val to 1 if not probe function
is implemented. Currently all probe functions only return zero or
one, so remove them all.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-21 16:54:00 +05:30
Xiang W
767b5fc418 lib: sbi: Optimize probe of srst/susp
No need to do a fully comprehensive count, just find a supported reset
or suspend type

Signed-off-by: Xiang W <wxjstz@126.com>
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-21 16:53:38 +05:30
Andrew Jones
8b952d4fcd lib: sbi: Only register available extensions
When an extension implements a probe function it means there's a
chance that the extension is not available. Use this function in the
register_extensions callback to determine if the extension should be
registered at all. Where the probe implementation is simple, just
open code the check.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-21 16:53:02 +05:30
Andrew Jones
042f0c3ea2 lib: sbi: pmu: Remove unnecessary probe function
The absence of a probe implementation means that the extension is
always available. Remove the implementation for the PMU extension,
which does no checking, and indeed even has a comment saying it's
always available.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-21 16:30:29 +05:30
Andrew Jones
e307ba7d46 lib: sbi: Narrow vendor extension range
The vendor extension ID range is large, but at runtime at most
a single ID will be available. Narrow the range in the
register_extensions callback. After narrowing, we no longer
need to check that the extension ID is correct in the other
callbacks, as those callbacks will never be invoked with
anything other than the single ID.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-21 16:29:46 +05:30
Andrew Jones
f58c14090f lib: sbi: Introduce register_extensions extension callback
Rather than registering all extensions on their behalf in
sbi_ecall_init(), introduce another extension callback and
invoke that instead. For now, implement each callback by
simply registering the extension, which means this patch
has no intended functional change. In later patches, extension
callbacks will be modified to choose when to register and to
possibly narrow the extension ID range prior to registering.
When an extension range needs to remove IDs, leaving gaps, then
multiple invocations of sbi_ecall_register_extension() may be
used. In summary, later patches for current extensions and the
introductions of future extensions will use the new callback to
ensure that only valid extension IDs from the initial range,
which are also available, will be registered.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-21 16:27:38 +05:30
Xiang W
6bc02dede8 lib: sbi: Simplify sbi_ipi_process remove goto
Simplify sbi_ipi_process() by removing goto statement.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-11 12:46:42 +05:30
Xiang W
4e3353057a lib: sbi: Remove unnecessary semicolon
We have redundant semicolon at quite a few places so let's remove it.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-05-11 12:31:34 +05:30
Tan En De
7919530308 lib: sbi: Add debug print when sbi_pmu_init fails
Since sbi_pmu_init is called after sbi_console_init,
the sbi_printf can be called when sbi_pmu_init fails.

Signed-off-by: Tan En De <ende.tan@starfivetech.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
2023-04-20 14:19:44 +05:30
Anup Patel
f5dfd99139 lib: sbi: Don't check SBI error range for legacy console getchar
The legacy console getchar SBI call returns character value in
the sbiret.error field so the "SBI_SUCCESS < ret" check in
sbi_ecall_handler() results in unwanted error prints for the
legacy console getchar SBI call. Let's suppress these unwanted
error prints.

Fixes: 67b2a40892 ("lib: sbi: sbi_ecall: Check the range of
SBI error")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
2023-04-17 09:48:13 +05:30
Alexandre Ghiti
674e0199b2 lib: sbi: Fix counter index calculation for SBI_PMU_CFG_FLAG_SKIP_MATCH
As per the SBI specification, we should "unconditionally select the first
counter from the set of counters specified by the counter_idx_base and
counter_idx_mask", so implement this behaviour.

Suggested-by: Atish Patra <atishp@atishpatra.org>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
2023-04-17 09:26:28 +05:30
Alexandre Ghiti
bdb3c42bca lib: sbi: Do not clear active_events for cycle/instret when stopping
Those events are enabled by default and should not be reset afterwards
since when using SBI_PMU_CFG_FLAG_SKIP_MATCH, it leads to unaccessible
counters after the first use.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
2023-04-17 09:26:26 +05:30
Xiang W
bf40e07f6f lib: sbi: Optimize sbi_tlb queue waiting
When tlb_fifo is full, it will wait and affect the ipi update to
other harts. This patch is optimized.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anup Patel <anup@brainfault.org>
2023-04-14 13:45:30 +05:30
Xiang W
80078ab088 sbi: tlb: Simplify to tlb_process_count/tlb_process function
tlb_process_count is only used when count=1, so refactor to
tlb_process_once and add the return value to be reused in
tlb_process

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anup Patel <anup@brainfault.org>
2023-04-13 13:49:57 +05:30
Xiang W
24dde46b8d lib: sbi: Optimize sbi_ipi
The original sbi_ipi will be processed by hart by hart, after optimization,
send ipi first and finally wait together.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anup Patel <anup@brainfault.org>
2023-04-13 12:44:50 +05:30
Xiang W
66fa925353 lib: sbi: Optimize sbi_tlb
Originally, the process and sync of sbi_tlb need to wait for each other.
Evasion by atomic addition and subtraction.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anup Patel <anup@brainfault.org>
2023-04-13 12:37:55 +05:30
Yu Chien Peter Lin
edc9914392 lib: sbi_pmu: Align the event type offset as per SBI specification
The bits encoded in event_idx[19:16] indicate the event type, with
an offset of 16 instead of 20.

Fixes: 13d40f21d5 ("lib: sbi: Add PMU support")
Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
2023-04-07 10:06:59 +05:30
Sunil V L
91767d093b lib: sbi: Print the CPPC device name
If CPPC device is registered by the platform, print its name.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-04-07 09:36:42 +05:30
Sunil V L
33caae8069 lib: sbi: Implement SBI CPPC extension
Implement SBI CPPC extension. This extension is only available when
OpenSBI platform provides a CPPC device to generic library.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-04-07 09:36:01 +05:30
Mayuresh Chitale
8e90259da8 lib: sbi_hart: clear mip csr during hart init
If mip.SEIP bit is not cleared then on HiFive Unmatched board it causes
spurious external interrupts. This breaks the boot up of HiFive Unmatched
board. Hence it is required to bring the mip CSR to a known state during
hart init and avoid spurious interrupts.

Fixes: d9e7368 ("firmware: Not to clear all the MIP")
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-04-06 18:52:03 +05:30
Anup Patel
30b9e7ee14 lib: sbi_hsm: Fix sbi_hsm_hart_start() for platform with hart hotplug
It possible that a platform supports hart hotplug (i.e. both hart_start
and hart_stop callbacks available) and all harts are start simultaneously
at platform boot-time. In this situation, the sbi_hsm_hart_start() will
call hsm_device_hart_start() for secondary harts at platform boot-time
which will fail because secondary harts were already started.

To fix above, we call hsm_device_hart_start() from sbi_hsm_hart_start()
only when entry_count is same as init_count for the secondary hart.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
2023-04-06 18:48:19 +05:30
Anup Patel
f64dfcd2b5 lib: sbi: Introduce sbi_entry_count() function
We introduce sbi_entry_count() function which counts the number
of times a HART enters OpenSBI via cold-boot or warm-boot path.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
2023-04-06 18:48:15 +05:30
Xiang W
73ab11dfb0 lib: sbi: Fix how to check whether the domain contains fw_region
Because firmware is split into rw/rx segments, it cannot be recorded
by a root_fw_region. This problem is solved by adding a flag
fw_region_inited to sbi_domain.

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Himanshu Chauhan <hchauhan@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-04-06 16:14:35 +05:30
Xiang W
ed88a63b90 lib: sbi_scratch: Optimize the alignment code for alloc size
Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-04-06 16:00:45 +05:30
Evgenii Shatokhin
c6a092cd80 lib: sbi: Clear IPIs before init_warm_startup in non-boot harts
Since commit 50d4fde1c5 ("lib: Remove redundant sbi_platform_ipi_clear()
calls"), the IPI sent from the boot hart in wake_coldboot_harts() is not
cleared in the secondary harts until they reach sbi_ipi_init(). However,
sbi_hsm_init() and sbi_hsm_hart_wait() are called earlier, so a secondary
hart might enter sbi_hsm_hart_wait() with an already pending IPI.

sbi_hsm_hart_wait() makes sure the hart leaves the loop only when it is
actually ready, so a pending unrelated IPI should not cause safety issues.
However, it might be inefficient on certain hardware, because it prevents
"wfi" from stalling the hart even if the hardware supports this, making the
hart needlessly spin in a "busy-wait" loop.

This behaviour can be observed, for example, in a QEMU VM (QEMU 7.2.0) with
"-machine virt" running a Linux guest. Inserting delays in
sbi_hsm_hart_start() allows reproducing the issue more reliably.

The comment in wait_for_coldboot() suggests that the initial IPI is needed
in the warm resume path, so let us clear it before init_warm_startup()
only.

To do this, sbi_ipi_raw_clear() was created similar to sbi_ipi_raw_send().

Signed-off-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-03-10 14:13:40 +05:30
Evgenii Shatokhin
e8e9ed3790 lib: sbi: Set the state of a hart to START_PENDING after the hart is ready
When a boot hart executes sbi_hsm_hart_start() to start a secondary hart,
next_arg1, next_addr and next_mode for the latter are stored in the scratch
area after the state has been set to SBI_HSM_STATE_START_PENDING.

The secondary hart waits in the loop with wfi() in sbi_hsm_hart_wait() at
that time. However, "wfi" instruction is not guaranteed to wait for an
interrupt to be received by the hart, it is just a hint for the CPU.
According to RISC-V Privileged Architectures spec. v20211203, even an
implementation of "wfi" as "nop" is legal.

So, the secondary might leave the loop in sbi_hsm_hart_wait() as soon as
its state has been set to SBI_HSM_STATE_START_PENDING, even if it got no
IPI or it got an IPI unrelated to sbi_hsm_hart_start(). This could lead to
the following race condition when booting Linux, for example:

  Boot hart (#0)                        Secondary hart (#1)
  runs Linux startup code               waits in sbi_hsm_hart_wait()

  sbi_ecall(SBI_EXT_HSM,
            SBI_EXT_HSM_HART_START,
            ...)
  enters sbi_hsm_hart_start()
  sets state of hart #1 to START_PENDING
                                        leaves sbi_hsm_hart_wait()
                                        runs to the end of init_warmboot()
                                        returns to scratch->next_addr
                                        (next_addr can be garbage here)

  sets next_addr, etc. for hart #1
  (no good: hart #1 has already left)

  sends IPI to hart #1
  (no good either)

If this happens, the secondary hart jumps to a wrong next_addr at the end
of init_warmboot(), which leads to a system hang or crash.

To reproduce the issue more reliably, one could add a delay in
sbi_hsm_hart_start() after setting the hart's state but before sending
IPI to that hart:

    hstate = atomic_cmpxchg(&hdata->state, SBI_HSM_STATE_STOPPED,
                            SBI_HSM_STATE_START_PENDING);
    ...
  + sbi_timer_mdelay(10);
    init_count = sbi_init_count(hartid);
    rscratch->next_arg1 = arg1;
    rscratch->next_addr = saddr;

The issue can be reproduced, for example, in a QEMU VM with '-machine virt'
and 2 or more CPUs, with Linux as the guest OS.

This patch moves writing of next_arg1, next_addr and next_mode for the
secondary hart before setting its state to SBI_HSM_STATE_START_PENDING.

In theory, it is possible that two or more harts enter sbi_hsm_hart_start()
for the same target hart simultaneously. To make sure the current hart has
exclusive access to the scratch area of the target hart at that point, a
per-hart 'start_ticket' is used. It is initially 0. The current hart tries
to acquire the ticket first (set it to 1) at the beginning of
sbi_hsm_hart_start() and only proceeds if it has successfully acquired it.

The target hart reads next_addr, etc., and then the releases the ticket
(sets it to 0) before calling sbi_hart_switch_mode(). This way, even if
some other hart manages to enter sbi_hsm_hart_start() after the ticket has
been released but before the target hart jumps to next_addr, it will not
cause problems.

atomic_cmpxchg() already has "acquire" semantics, among other things, so
no additional barriers are needed in hsm_start_ticket_acquire(). No hart
can perform or observe the update of *rscratch before setting of
'start_ticket' to 1.

atomic_write() only imposes ordering of writes, so an explicit barrier is
needed in hsm_start_ticket_release() to ensure its "release" semantics.
This guarantees that reads of scratch->next_addr, etc., in
sbi_hsm_hart_start_finish() cannot happen after 'start_ticket' has been
released.

Signed-off-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
2023-03-10 14:12:43 +05:30