On 3/19/2024 3:52 PM, Pavan Kondeti wrote:
On Tue, Mar 19, 2024 at 03:38:57PM +0530, Mukesh Ojha wrote:
On 3/19/2024 6:47 AM, Pavan Kondeti wrote:
On Mon, Mar 18, 2024 at 06:38:20PM +0530, Mukesh Ojha wrote:
On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
qcom_scm_is_available() gives wrong indication if __scm
is initialized but __scm->dev is not.
Fix this appropriately by making sure if __scm is
initialized and then it is associated with its
device.
This seems like a bug fix, and should as such have a Fixes: tag and
probably Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
---
drivers/firmware/qcom/qcom_scm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index 6c252cddd44e..6f14254c0c10 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
if (!scm)
return -ENOMEM;
+ scm->dev = &pdev->dev;
ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
if (ret < 0)
return ret;
@@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
return ret;
__scm = scm;
- __scm->dev = &pdev->dev;
Is it sufficient to just move the line up, or do we need a barrier of
some sort here?
Would be good to use, smp_mb() before the assignment
__scm = scm
along with moving below line
__scm->dev = &pdev->dev
Full memory barrier is not needed here. store variant is sufficient.
WRITE_ONCE() + smp_store_release() will fit here no?
Thanks for the comment, i again have a look at it and agree we don't
need a full barrier here.
And we can do either of the below two ways.
-Mukesh
// 1st way
diff --git a/drivers/firmware/qcom/qcom_scm.c
b/drivers/firmware/qcom/qcom_scm.c
index 49ddbcab0680..b638fb407fc6 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1741,7 +1741,12 @@ static int qcom_scm_qseecom_init(struct qcom_scm
*scm)
*/
bool qcom_scm_is_available(void)
{
- return !!__scm;
+ bool avail;
*/
bool qcom_scm_is_available(void)
{
- return !!__scm;
+ bool avail;
+
+ avail = !!READ_ONCE(__scm);
+ smp_rmb();
+
+ return avail;
}
EXPORT_SYMBOL_GPL(qcom_scm_is_available);
Your original problem statement: qcom_scm_is_available() gives wrong indication
if __scm is initialized but __scm->dev is not.
This does not require read side barrier as there is an address
dependency. If the writer does it *correctly*, the reader would always
observe __scm->dev != NULL when __scm != NULL without any barrier.
It looks like write barrier pairs with an address-dependency barrier, a
control dependency, an acquire barrier, a release barrier, a read
barrier, or a general barrier.
So, smp_rmb() is redundant here.
Also, for correction, we may not need smp_load_acquire() in the 1st way
and just using READ_ONCE() is enough.
-Mukesh
Thanks,
Pavan
