Re: [PATCH RFC v3 08/11] scsi: ufs: core: Perform read back after disabling interrupts

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On 12/22/2023 3:09 AM, Andrew Halaney wrote:
Currently, interrupts are cleared and disabled prior to registering the
interrupt. An mb() is used to complete the clear/disable writes before
the interrupt is registered.

mb() ensure that the write completes, but completion doesn't mean that
it isn't stored in a buffer somewhere. The recommendation for
ensuring these bits have taken effect on the device is to perform a read
back to force it to make it all the way to the device. This is
documented in device-io.rst and a talk by Will Deacon on this can
be seen over here:

Let's do that to ensure these bits hit the device. Because the mb()'s
purpose wasn't to add extra ordering (on top of the ordering guaranteed
by writel()/readl()), it can safely be removed.

Fixes: 199ef13cac7d ("scsi: ufs: avoid spurious UFS host controller interrupts")
Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
  drivers/ufs/core/ufshcd.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 7bfb556e5b8e..bb603769b029 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -10568,7 +10568,7 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
  	 * Make sure that UFS interrupts are disabled and any pending interrupt
  	 * status is cleared before registering UFS interrupt handler.
-	mb();
+	ufshcd_readl(hba, REG_INTERRUPT_ENABLE);
/* IRQ registration */
  	err = devm_request_irq(dev, irq, ufshcd_intr, IRQF_SHARED, UFSHCD, hba);

Reviewed-by: Can Guo <quic_cang@xxxxxxxxxxx>

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