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

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Date:   Mon, 29 Oct 2018 19:43:56 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     Dmitry Torokhov <dtor@...gle.com>,
        "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>,
        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 29, 2018 at 10:22:02AM -0700, Rajat Jain wrote:
> On Mon, Oct 29, 2018 at 8:23 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Wed, Oct 24, 2018 at 9:03 PM Dmitry Torokhov <dtor@...gle.com> wrote:
> > > On Wed, Oct 24, 2018 at 3:02 AM Andy Shevchenko
> > > <andy.shevchenko@...il.com> wrote:
> > > > 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:

> > > > > Also, the driver may not
> > > > > really know?
> > > >
> > > > I think in such case the bug in HW design and / or driver.
> > >
> > > Why? You can have a shared or dedicated interrupt and the driver does
> > > not really need to know if it can poll the status.
> >
> > Yes, that's my point either we get 1:1 mapping between slot and GPIOs
> > or have a possibility to read back from some register(s) the actual
> > status of all of them, otherwise it's a bad design.
> 
> No, AFAIU, the driver only should only be able to read the status of
> *the* interrupt that was fired? (as opposite to the ability to read
> *all of them* when an interrupt fires).

I can't be sure in the details of this (sdhci) driver, I'm not a maintainer of
that one. So, my above conclusions are purely generic.

> > > > > 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.
> > >
> > > Again, you think as if the driver was platform specific; it is not. I
> > > have 1000s of systems with different ACPI tables. Let's say half of
> > > them use one polarity, and half another. Which polarity do you propose
> > > to use?
> >
> > Use one table for one half and another for the rest.
> 
> But how does driver determine which table to use for which platform?
> (Currently the driver is platform independent).

Based on vendor and device IDs in any form of it.

-- 
With Best Regards,
Andy Shevchenko