Re: [PATCH RFC v3 11/11] scsi: ufs: core: Perform read back before writing run/stop regs

[Bart Van Assche]

On 12/21/23 11:09, Andrew Halaney wrote:
> Currently a wmb() is used to ensure that writes to the
> UTP_TASK_REQ_LIST_BASE* regs are completed prior to following writes to
> the run/stop registers.
>
> wmb() ensure that the write completes, but completion doesn't mean that
> it isn't stored in a buffer somewhere. The recommendation for
> ensuring the 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 the bits hit the device. Because the wmb()'s
> purpose wasn't to add extra ordering (on top of the ordering guaranteed
> by writel()/readl()), it can safely be removed.

Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>