Re: [PATCH v3] mmc: mtk-sd: reduce CIT for better performance

[AngeloGioacchino Del Regno]

Il 06/06/23 10:17, Wenbin Mei (梅文彬) ha scritto:
> On Mon, 2023-06-05 at 10:48 +0200, AngeloGioacchino Del Regno wrote:
> >   	
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> >   Il 05/06/23 08:01, Wenbin Mei ha scritto:
> > > CQHCI_SSC1 indicates to CQE the polling period to use when using
> > periodic
> > > SEND_QUEUE_STATUS(CMD13) polling.
> > > Since MSDC CQE uses msdc_hclk as ITCFVAL, so driver should use hclk
> > > frequency to get the actual time.
> > > The default value 0x1000 that corresponds to 150us for MediaTek
> > SoCs, let's
> > > decrease it to 0x40 that corresponds to 2.35us, which can improve
> > the
> > > performance of some eMMC devices.
> > >
> > > Signed-off-by: Wenbin Mei <wenbin.mei@xxxxxxxxxxxx>
> >
> > OK! That's almost good now. There's only one consideration here: if
> > MediaTek
> > SoCs *require* msdc_hclk to calculate the CIT time, this means that
> > this clock
> > is critical for CQHCI functionality.
> >
> > If msdc_hclk is not present, CQHCI cannot work correctly... so you
> > don't have
> > to cover the case in which there's no msdc_hclk clock: if that's not
> > present,
> > either fail probing, or disable CQHCI.
> >
> > > ---
> > >    drivers/mmc/host/cqhci.h  |  1 +
> > >    drivers/mmc/host/mtk-sd.c | 47
> > +++++++++++++++++++++++++++++++++++++++
> > >    2 files changed, 48 insertions(+)
> > >
> > > diff --git a/drivers/mmc/host/cqhci.h b/drivers/mmc/host/cqhci.h
> > > index ba9387ed90eb..292b89ebd978 100644
> > > --- a/drivers/mmc/host/cqhci.h
> > > +++ b/drivers/mmc/host/cqhci.h
> > > @@ -23,6 +23,7 @@
> > >    /* capabilities */
> > >    #define CQHCI_CAP0x04
> > >    #define CQHCI_CAP_CS0x10000000 /* Crypto Support */
> > > +#define CQHCI_CAP_ITCFMUL(x)(((x) & GENMASK(15, 12)) >> 12)
> > >    
> > >    /* configuration */
> > >    #define CQHCI_CFG0x08
> > > diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
> > > index edade0e54a0c..c221ef8a6992 100644
> > > --- a/drivers/mmc/host/mtk-sd.c
> > > +++ b/drivers/mmc/host/mtk-sd.c
> > > @@ -473,6 +473,7 @@ struct msdc_host {
> > >    struct msdc_tune_para def_tune_para; /* default tune setting */
> > >    struct msdc_tune_para saved_tune_para; /* tune result of
> > CMD21/CMD19 */
> > >    struct cqhci_host *cq_host;
> > > +u32 cq_ssc1_time;
> > >    };
> > >    
> > >    static const struct mtk_mmc_compatible mt2701_compat = {
> > > @@ -2450,9 +2451,50 @@ static void
> > msdc_hs400_enhanced_strobe(struct mmc_host *mmc,
> > >    }
> > >    }
> > >    
> > > +static void msdc_cqe_cit_cal(struct msdc_host *host, u64 timer_ns)
> >
> > static int msdc_cqe_cit_cal(....)
> Sorry, I missed this comment.
> I think there is no need to return a value.
> Becuase msdc_hclk is exist, and if not present, it will return earily.
> Even if it goes to the default case in the switch flow, we will assign
> a default value.
> So I think it's better to return null, do you think it is okay?

Yeah ignore this comment; I've noticed that HCLK is already mandatory, otherwise
the probe function will fail earlier anyway.

Thanks,
Angelo