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soc: qcom: smem: remove hwspinlock from item get routine

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During an SSR(Sub-System Restart) process, the remoteproc driver will
try to read the crash reason from SMEM. The qcom_smem_get() backing such
operations does however take the hwspinlock (tcsr mutex), which might be
held by the dying remoteproc.

The associated timeout on the hwspin_lock_timeout_irqsave() would take
care of the system not hanging forever, but the get operation will fail,
unnecessarily delaying the process for the 'HWSPINLOCK_TIMEOUT' duration
(currently is '1s'), and finally resulting in failure to get crash
information from SMEM.

This timeout can be avoided by removing the hwspinlock in the
qcom_smem_get routine. SMEM ensures that the allocated item will only be
visible after the new item is safe to use by following a specific order
of updates.

In the private partition case, qcom_smem_get_private() will use
'offset_free_uncached' as a loop boundary when looking for existing
allocated items. The corresponding allocation will only update
offset_free_uncached once the item is fully initialized.

    hdr->canary = SMEM_PRIVATE_CANARY;
    hdr->item = cpu_to_le16(item);
    hdr->size = cpu_to_le32(ALIGN(size, 8));
    hdr->padding_data = cpu_to_le16(le32_to_cpu(hdr->size) - size);
    hdr->padding_hdr = 0;

    wmb();
    le32_add_cpu(&phdr->offset_free_uncached, alloc_size);

The global partition is similar but uses the "entry->allocated" variable
to ensure the item is not visible to qcom_smem_get_global().

Signed-off-by: Tao Zhang <quic_taozhan@quicinc.com>
Reviewed-by: Chris Lew <quic_clew@quicinc.com>
Link: https://lore.kernel.org/r/20240102022512.999635-1-quic_taozhan@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
This commit is contained in:
Tao Zhang 2024-01-02 07:55:12 +05:30 committed by Bjorn Andersson
parent 8796fa0f9a
commit 27825593c9
1 changed files with 0 additions and 11 deletions
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11
drivers/soc/qcom/smem.c
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@ -655,8 +655,6 @@ static void *qcom_smem_get_private(struct qcom_smem *smem,
void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
{
struct smem_partition *part;
unsigned long flags;
int ret;
void *ptr = ERR_PTR(-EPROBE_DEFER);
if (!__smem)
@ -665,12 +663,6 @@ void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
if (WARN_ON(item >= __smem->item_count))
return ERR_PTR(-EINVAL);
ret = hwspin_lock_timeout_irqsave(__smem->hwlock,
HWSPINLOCK_TIMEOUT,
&flags);
if (ret)
return ERR_PTR(ret);
if (host < SMEM_HOST_COUNT && __smem->partitions[host].virt_base) {
part = &__smem->partitions[host];
ptr = qcom_smem_get_private(__smem, part, item, size);
@ -681,10 +673,7 @@ void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
ptr = qcom_smem_get_global(__smem, item, size);
}
hwspin_unlock_irqrestore(__smem->hwlock, &flags);
return ptr;
}
EXPORT_SYMBOL_GPL(qcom_smem_get);