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[RFC,v2,08/11] scsi: ufs: core: Perform read back after disabling interrupts

Message ID 20231221-ufs-reset-ensure-effect-before-delay-v2-8-75af2a9bae51@redhat.com
State Superseded
Headers show
Series scsi: ufs: Remove overzealous memory barriers | expand

Commit Message

Andrew Halaney Dec. 21, 2023, 6:25 p.m. UTC
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:

    https://youtu.be/i6DayghhA8Q?si=MiyxB5cKJXSaoc01&t=1678

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@redhat.com>
---
 drivers/ufs/core/ufshcd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Manivannan Sadhasivam Dec. 27, 2023, 6:13 a.m. UTC | #1
On Thu, Dec 21, 2023 at 12:25:25PM -0600, 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:
> 
>     https://youtu.be/i6DayghhA8Q?si=MiyxB5cKJXSaoc01&t=1678
> 
> 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@redhat.com>

Same comment as patch 07/11.

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

- Mani

> ---
>  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);
> 
> -- 
> 2.43.0
>
diff mbox series

Patch

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);