linux-kernel - Re: [PATCH] mmc: block: enable cache-flushing when mmc cache is on

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Message-ID: <CAPDyKFqnFVd=mvQMnydT569Y6YFg3zPkttQ=amdzmT_yqYQeTg@mail.gmail.com>
Date:   Thu, 24 Mar 2022 12:27:05 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Michael Wu <michael@...winnertech.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Christian Löhle <CLoehle@...erstone.com>,
        Avri Altman <avri.altman@....com>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "porzio@...il.com" <porzio@...il.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        allwinner-opensource-support 
        <allwinner-opensource-support@...winnertech.com>
Subject: Re: [PATCH] mmc: block: enable cache-flushing when mmc cache is on

On Thu, 17 Mar 2022 at 10:14, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Wed, 16 Mar 2022 at 17:08, Adrian Hunter <adrian.hunter@...el.com> wrote:
> >
> > On 16.3.2022 16.46, Christian Löhle wrote:
> > >> So we are not going to let the block layer know about SD cache?
> > >> Or is it a separate change?
> > >
> > > I have some code for this laying around, but as it requires reading, parsing and writing Function Registers,
> > > in particular PEH, it's a lot of boilerplate code to get the functionality, but I'll clean it up and send a patch in the coming weeks.
> > >
> >
> > We have the sd cache flush.  We would presumably just need to call blk_queue_write_cache()
> > for the !mmc_card_mmc(card) case e.g.
> >
> >         if (mmc_has_reliable_write(card)) {
> >                 md->flags |= MMC_BLK_REL_WR;
> >                 enable_fua = true;
> >         }
> >
> >         if (mmc_cache_enabled(card->host))
> >                 enable_cache = true;
> >
> >         blk_queue_write_cache(md->queue.queue, enable_cache, enable_fua);
>
> To me, this seems like the most reasonable thing to do.
>
> However, I have to admit that it's not clear to me, if there was a
> good reason to why commit f4c5522b0a88 ("mmc: Reliable write
> support.") also added support for REQ_FLUSH (write back cache) and why
> not only REQ_FUA. I assumed this was wrong too, right?
>
> When it comes to patches for stable kernels. mmc_cache_enabled() was
> introduced quite recently in v5.13, so for older kernels that call
> needs to be replaced with something else.
>
> In any case, the relevant commits that can be considered as needs to
> be fixed seems like these:
> commit f4c5522b0a88 ("mmc: Reliable write support.")
> commit 881d1c25f765 ("mmc: core: Add cache control for eMMC4.5 device")
> commit 130206a615a9 ("mmc: core: Add support for cache ctrl for SD cards")
>
> [...]

Michael, are you planning to send a v2 for this? Or are there any
parts that are still unclear to you?

Kind regards
Uffe