linux-kernel - Re: [PATCH] mmc: sdhci-pci: Try "cd" for card-detect lookup before using NULL

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Date:   Wed, 24 Oct 2018 13:02:30 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     "Hunter, Adrian" <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Rajat Jain <rajatxjain@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Dmitry Torokhov <dtor@...gle.com>, linux-gpio@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH] mmc: sdhci-pci: Try "cd" for card-detect lookup before
 using NULL

On Mon, Oct 22, 2018 at 04:34:55PM -0700, Rajat Jain wrote:
> On Fri, Oct 19, 2018 at 2:13 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Fri, Oct 19, 2018 at 12:53 AM Rajat Jain <rajatja@...gle.com> wrote:

> > > across other users of this API (other MMC host controller drivers).
> >
> > >         if (slot->cd_idx >= 0) {
> > > -               ret = mmc_gpiod_request_cd(host->mmc, NULL, slot->cd_idx,
> > > +               ret = mmc_gpiod_request_cd(host->mmc, "cd", slot->cd_idx,
> > >                                            slot->cd_override_level, 0, NULL);
> >
> > Yes.
> >
> > > +               if (ret && ret != -EPROBE_DEFER)
> > > +                       ret = mmc_gpiod_request_cd(host->mmc, NULL,
> > > +                                                  slot->cd_idx,
> > > +                                                  slot->cd_override_level,
> > > +                                                  0, NULL);
> >
> > And no. Instead of this part you need to provide an ACPI GPIO mapping table.
> 
> Sure, I am willing to do so, and I tried earlier too. However, certain
> doubts arose in my mind when I tried that and I posted my questions
> earlier (https://lkml.org/lkml/2018/9/28/507) but couldn't elicit any
> response. Unfortunately I still do not have answers. My primary
> questions are:
> 
> 1) - It seems that 1 SDHCI device may support multiple slots (looking
> at the code). It is not clear to me if they could share card detect
> interrupts, or should have separate ones? 

This is more likely question to HW engineers of your platform with a caveat
that there should be a way to distinguish exact slot in which card is being
inserted.

> Also, the driver may not
> really know? 

I think in such case the bug in HW design and / or driver.

> So should I add 1 or two pins using the
> devm_acpi_dev_add_driver_gpios().

This depends on the above, e.g. HW design, ACPI tables.

> Is some one familiar with SDHC
> driver can answer these questions, it shall be great.

Actually above questions better to ask in linux-mmc mailing list, which by the
fact is in Cc list already. So, wait for someone to clarify.


> 2) I'm not really sure what should I set "active_low" to? Isn't this
> something that should be specified by platform / ACPI too, and driver
> should just be able to say say choose whatever the ACPI says?
> 
> struct acpi_gpio_params {
>         unsigned int crs_entry_index;
>         unsigned int line_index;
>         bool active_low;
> };


ACPI specification misses this property, that's why we have it in the
structure. In your case it should be provided by _DSD and thus be consistent
with the hardcoded values.

> Since I do not understand the above two issues, and thus I chose the
> safest path and not disturb the current code so as not to cause any
> regressions.

As far as I can see in the above it is disturbing the current code more than
needed.

> 
> Please let me know, and I'm happy to re-spin my patch.

-- 
With Best Regards,
Andy Shevchenko