Re: [RFC PATCH] mmc: core: Disable REQ_FUA if the eMMC supports an internal cache

[Bean Huo]

On 02.03.23 3:43 PM, Ulf Hansson wrote:
> REQ_FUA is in general supported for eMMC cards, which translates into so
> called "reliable writes". To support these write operations, the CMD23
> (MMC_CAP_CMD23), needs to be supported by the mmc host too, which is common
> but not always the case.
>
> For some eMMC devices, it has been reported that reliable writes are quite
> costly, leading to performance degradations.
>
> In a way to improve the situation, let's avoid announcing REQ_FUA support
> if the eMMC supports an internal cache, as that allows us to rely solely on
> flush-requests (REQ_OP_FLUSH) instead, which seems to be a lot cheaper.
> Note that, those mmc hosts that lacks CMD23 support are already using this
> type of configuration, whatever that could mean.
>
> Reported-by: Wenchao Chen<wenchao.chen666@xxxxxxxxx>
> Signed-off-by: Ulf Hansson<ulf.hansson@xxxxxxxxxx>
Acked-by: Bean Huo <beanhuo@xxxxxxxxxx>