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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Fri, 27 Oct 2023 11:53:26 +0200
Message-ID: <CAPDyKFrVNfqUxU2iGEDXrshOEKm1KROCHTPpSyDAgZPMPojfsg@mail.gmail.com>
Subject: Re: [PATCH V3 1/3] mmc: core: Add partial initialization support
To:     Sarthak Garg <quic_sartgarg@quicinc.com>
Cc:     Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, quic_cang@quicinc.com,
        quic_nguyenb@quicinc.com, quic_rampraka@quicinc.com,
        quic_pragalla@quicinc.com, quic_sayalil@quicinc.com,
        quic_nitirawa@quicinc.com, quic_sachgupt@quicinc.com,
        quic_bhaskarv@quicinc.com, quic_narepall@quicinc.com,
        kernel@quicinc.com,
        Veerabhadrarao Badiganti <quic_vbadigan@quicinc.com>
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[...]

> >> +{
> >> +       int err = 0;
> >> +       struct mmc_card *card = host->card;
> >> +
> >> +       mmc_set_bus_width(host, host->cached_ios.bus_width);
> >> +       mmc_set_timing(host, host->cached_ios.timing);
> >> +       if (host->cached_ios.enhanced_strobe) {
> >> +               host->ios.enhanced_strobe = true;
> >> +               if (host->ops->hs400_enhanced_strobe)
> >> +                       host->ops->hs400_enhanced_strobe(host, &host->ios);
> >> +       }
> >> +       mmc_set_clock(host, host->cached_ios.clock);
> >> +       mmc_set_bus_mode(host, host->cached_ios.bus_mode);
> >> +
> >
> > Rather than re-using the above APIs and the ->set_ios() callback in
> > the host, I believe it would be better to add a new host ops to manage
> > all of the above at once instead. Something along the lines of the
> > below, would then replace all of the above.
> >
> > host->ops->restore_ios(host, &host->cached_ios)
> > memcpy(&host->ios, &host->cached_ios, sizeof(host->ios));
> >
> > Would that make sense to you too?
> >
>
>
> I didn't get this completely. Do you mean that we should implement a new
> restore_ios callback (e.g. sdhci_restore_ios) similar to sdhci_set_ios
> and removing all the redundant code from sdhci_set_ios which should
> achieve the behaviour same as calling all the above mmc_set_* API's ?

Correct. Would it not simply the things in the driver too?

>
>
> >> +       if (!mmc_card_hs400es(card) &&
> >> +                       (mmc_card_hs200(card) || mmc_card_hs400(card))) {
> >> +               err = mmc_execute_tuning(card);
> >> +               if (err) {
> >> +                       pr_err("%s: %s: Tuning failed (%d)\n",
> >> +                               mmc_hostname(host), __func__, err);
> >
> > There is already a print being done in mmc_execute_tuning() at
> > failure. So, let's drop the above print.
> >
>
> Sure will take care in V4.
>
> >> +                       goto out;
> >> +               }
> >> +       }
> >> +
> >> +       err = mmc_test_awake_ext_csd(host);
> >
> > Again, I don't get why this is needed, so let's discuss this more.
> >
>
> This is just a safety check added because ext_csd has some W/E_P or
> W/C_P registers which gets reset if any HW reset happens to the card.
> So this will check for those cases if any other vendor is doing reset as
> part of suspend and compare a subset of those W/E_P and W/C_P registers
> and if they are changed then we will bail out of this partial init
> feature and go for full initialization.
> We are also fine with removing this function but just added for the
> above mentioned case.

In that case, I would rather remove it as I think it's superfluous.

More precisely, I would expect that we fail to wake up the card with a
CMD5 (get an error response for the CMD) if there has been a HW reset
somewhere done before.

Another reason to *not* read the ext_csd would be to further improve
the resume time, as reading it takes time too. I would be curious to
know how much though. :-)

[...]

Kind regards
Uffe