On Thu, Dec 21, 2023 at 12:25:21PM -0600, Andrew Halaney wrote:
> Currently, the QUNIPRO_SEL bit is written to and then an mb() is used to
> ensure that completes before continuing.
>
> mb() ensure that the write completes, but completion doesn't mean that
> it isn't stored in a buffer somewhere. The recommendation for
> ensuring this bit has 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 bit hits 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: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations")
> Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
> ---
> drivers/ufs/host/ufs-qcom.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
> index 6df2ab3b6f23..ab1ff7432d11 100644
> --- a/drivers/ufs/host/ufs-qcom.c
> +++ b/drivers/ufs/host/ufs-qcom.c
> @@ -280,7 +280,7 @@ static void ufs_qcom_select_unipro_mode(struct ufs_qcom_host *host)
> ufshcd_rmwl(host->hba, QUNIPRO_G4_SEL, 0, REG_UFS_CFG0);
>
> /* make sure above configuration is applied before we return */
> - mb();
> + ufshcd_readl(host->hba, REG_UFS_CFG1);
Same comment as patch 03/11.
- Mani
> }
>
> /*
>
> --
> 2.43.0
>
--
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