Commit 27825593 authored by Tao Zhang's avatar Tao Zhang Committed by Bjorn Andersson
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soc: qcom: smem: remove hwspinlock from item get routine 



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: default avatarTao Zhang <quic_taozhan@quicinc.com>
Reviewed-by: default avatarChris Lew <quic_clew@quicinc.com>
Link: https://lore.kernel.org/r/20240102022512.999635-1-quic_taozhan@quicinc.com


Signed-off-by: default avatarBjorn Andersson <andersson@kernel.org>
parent 8796fa0f

drivers/soc/qcom/smem.c

+0 −11
Original line number Diff line number Diff line
@@ -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);