linux-kernel - RE: [PATCH V2 1/2] mmc: block: Support Host to control FUA

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Date:   Fri, 21 Oct 2022 09:37:32 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Wenchao Chen <wenchao.chen666@...il.com>
CC:     "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "orsonzhai@...il.com" <orsonzhai@...il.com>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        "zhang.lyra@...il.com" <zhang.lyra@...il.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "kch@...dia.com" <kch@...dia.com>,
        "CLoehle@...erstone.com" <CLoehle@...erstone.com>,
        "vincent.whitchurch@...s.com" <vincent.whitchurch@...s.com>,
        "bigeasy@...utronix.de" <bigeasy@...utronix.de>,
        "s.shtylyov@....ru" <s.shtylyov@....ru>,
        "michael@...winnertech.com" <michael@...winnertech.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "megoo.tang@...il.com" <megoo.tang@...il.com>,
        "lzx.stg@...il.com" <lzx.stg@...il.com>
Subject: RE: [PATCH V2 1/2] mmc: block: Support Host to control FUA

> Avri Altman <Avri.Altman@....com> 于2022年10月21日周五 15:53写道：
> >
> > > From: Wenchao Chen <wenchao.chen@...soc.com>
> > >
> > > This patch introduces host->fua_disable for MMC host controller.
> > > The host can turn off FUA to improve performance.
> > >
> > > Signed-off-by: Wenchao Chen <wenchao.chen@...soc.com>
> > > ---
> > > V1 -> V2
> > > Address Chaitanyak's suggestions
> > > Address Avri's suggestions
> > > ---
> > >  drivers/mmc/core/block.c | 3 ++-
> > >  include/linux/mmc/host.h | 3 +++
> > >  2 files changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c index
> > > 54cd009aee50..333e819e077a 100644
> > > --- a/drivers/mmc/core/block.c
> > > +++ b/drivers/mmc/core/block.c
> > > @@ -2490,7 +2490,8 @@ static struct mmc_blk_data
> > > *mmc_blk_alloc_req(struct mmc_card *card,
> > >             ((card->ext_csd.rel_param & EXT_CSD_WR_REL_PARAM_EN) ||
> > >              card->ext_csd.rel_sectors)) {
> > >                 md->flags |= MMC_BLK_REL_WR;
> > > -               fua_enabled = true;
> > > +               if (!card->host->fua_disable)
> > > +                       fua_enabled = true;
> > >                 cache_enabled = true;
> > >         }
> > >         if (mmc_cache_enabled(card->host)) diff --git
> a/include/linux/mmc/host.h
> > > b/include/linux/mmc/host.h index 8fdd3cf971a3..16a5bee3eeae 100644
> > > --- a/include/linux/mmc/host.h
> > > +++ b/include/linux/mmc/host.h
> > > @@ -517,6 +517,9 @@ struct mmc_host {
> > >         struct blk_crypto_profile crypto_profile;  #endif
> > >
> > > +       /* Host FUA support */
> > > +       bool                    fua_disable;
> > Why do you need to invent a LLD mechanism, when you already have a block
> api (QUEUE_FLAG_FUA) for that?
> > Which is actually misleading, since /sys/block/mmcblk0/queue/fua will still
> reads 0.
> >
> > Thanks,
> > Avri
> >
> Hi Avri
> The code expands as follows:
> static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>       struct device *parent,
>       sector_t size,
>       bool default_ro,
>       const char *subname,
>       int area_type,
>       unsigned int part_type)
> {
> ...
> if (md->flags & MMC_BLK_CMD23 &&
>     ((card->ext_csd.rel_param & EXT_CSD_WR_REL_PARAM_EN) ||
>      card->ext_csd.rel_sectors)) {
> md->flags |= MMC_BLK_REL_WR;
> if (!card->host->fua_disable) <<<Allow chip manufacturers whether to use FUA.
> fua_enabled = true;
> cache_enabled = true;
> }
> if (mmc_cache_enabled(card->host))
> cache_enabled  = true;
> 
> blk_queue_write_cache(md->queue.queue, cache_enabled, fua_enabled); <<<
> ...
> }
> 
> void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
> {
> if (wc)
> blk_queue_flag_set(QUEUE_FLAG_WC, q);
> else
> blk_queue_flag_clear(QUEUE_FLAG_WC, q);
> if (fua)
> blk_queue_flag_set(QUEUE_FLAG_FUA, q);  <<<
> else
> blk_queue_flag_clear(QUEUE_FLAG_FUA, q);
> 
> wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
> }
Ahha - ok.
Thanks for clarifying this.

> 
> Also, echo 0 > fua is forbidden regardless of permissions.
> Do you have any better suggestions?
No - I see what you mean now.
Looks good to me.

Thanks,
Avri
> 
> > > +
> > >         /* Host Software Queue support */
> > >         bool                    hsq_enabled;
> > >
> > > --
> > > 2.17.1
> >