diff mbox series

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

Message ID 20231221-ufs-reset-ensure-effect-before-delay-v3-8-2195a1b66d2e@redhat.com
State New
Headers
Series scsi: ufs: Remove overzealous memory barriers |

Commit Message

Andrew Halaney Dec. 21, 2023, 7:09 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

Bart Van Assche Dec. 21, 2023, 7:30 p.m. UTC | #1 
On 12/21/23 11:09, 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>
> ---
>   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: Bart Van Assche <bvanassche@acm.org>
Can Guo Dec. 22, 2023, 8:26 a.m. UTC | #2 
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:
> 
>      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(-)
> 
> 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@quicinc.com>
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);