From: Rajat Jain <email@example.com>
To: Andy Shevchenko <firstname.lastname@example.org>
Cc: Mika Westerberg <email@example.com>,
Andy Shevchenko <firstname.lastname@example.org>,
Linus Walleij <email@example.com>,
Dmitry Torokhov <firstname.lastname@example.org>,
Linux Kernel Mailing List <email@example.com>,
"Hunter, Adrian" <firstname.lastname@example.org>,
Ulf Hansson <email@example.com>,
firstname.lastname@example.org, Rajat Jain <email@example.com>
Subject: Re: sdhci driver card-detect is broken because gpiolib can't fallback to _CRS?
Date: Thu, 27 Sep 2018 10:56:39 -0700 [thread overview]
Message-ID: <CACK8Z6HjFy_5sv_ZRRyfRgCYMYPpuoFqmKekyi7fSLk14YpN6w@mail.gmail.com> (raw)
On Thu, Sep 27, 2018 at 12:26 AM Andy Shevchenko
> On Wed, Sep 26, 2018 at 10:26 PM Rajat Jain <firstname.lastname@example.org> wrote:
> > On Wed, Sep 26, 2018 at 1:42 AM Andy Shevchenko
> > <email@example.com> wrote:
> > > On Wed, Sep 26, 2018 at 10:49 AM Mika Westerberg
> > > <firstname.lastname@example.org> wrote:
> > > > Or you can use con_id=<actual string> everywhere and supply
> > > > acpi_dev_add_driver_gpios() where needed to cover cases where BIOS does
> > > > not provide _DSD.
> > This sounds like a good idea and I'd like to do this. I have some
> > questions though:
> > 1) If the BIOS does provide a _DSD entry for "cd-gpio", and
> > additionally driver also uses devm_acpi_dev_add_driver_gpios() to add
> > one more entry for the same string "cd-gpio", which one will (should?)
> > actually be returned by the gpiolib? The one in BIOS or the one that
> > was added by the driver?
> Of course the one that BIOS provides. This hardcoded mapping tables is
> a fallback for *old* BIOSes which do not have _DSD.
> > 2) Related, I'm trying to understand how can a driver use
> > devm_acpi_dev_add_driver_gpios(), for *only* the case where the BIOS
> > does not have a _DSD (Or should it really care)? Does the driver need
> > to check for _DSD using some other ACPI call?
> The magic happens internally in ACPI core.
> Whenever one calls gpiod_get() with a name on ACPI-enabled platform,
> _DSD would be checked first.
Got it, thanks.
> > > See also Documentation/acpi/gpio-properties.txt for
> > > > more information.
> > > > In case of SDHCI I think the correct way is to stick using _CRS lookup
> > > > only because there typically is just one GpioInt() and I have not seen a
> > > > single BIOS yet where they implement _DSD for this besides yours. If
> > > > there is not way to change the BIOS implementation then I guess we just
> > > > need to amend the driver to call acpi_dev_add_driver_gpios().
> > Since we shouldn't discourage a BIOS that is trying to do the right
> > thing by exposing the details in _DST, I think it would be preferable
> > if we can solve this in the kernel.
> Patches are welcome, I think.
> Btw, is there any existing hardware on the market with such BIOS?
Yes, all the chrome books available in the market (at least the ones
released in last 3 years) have same ACPI layout (provide _DSD for
card-detect). They are all working fine today because they use an
older kernel, but if we update them to the latest kernel, this part
will be broken.
> With Best Regards,
> Andy Shevchenko
next prev parent reply other threads:[~2018-09-27 17:57 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-25 20:54 sdhci driver card-detect is broken because gpiolib can't fallback to _CRS? Rajat Jain
2018-09-26 7:47 ` Mika Westerberg
2018-09-26 8:42 ` Andy Shevchenko
2018-09-26 19:25 ` Rajat Jain
2018-09-27 7:26 ` Andy Shevchenko
2018-09-27 17:56 ` Rajat Jain [this message]
2018-09-28 8:42 ` Linus Walleij
2018-09-28 12:34 ` Rajat Jain
2018-09-28 13:13 ` Linus Walleij
2018-10-18 21:51 ` [PATCH] mmc: sdhci-pci: Try "cd" for card-detect lookup before using NULL Rajat Jain
2018-10-19 9:13 ` Andy Shevchenko
2018-10-22 23:34 ` Rajat Jain
2018-10-24 10:02 ` Andy Shevchenko
2018-10-24 18:03 ` Dmitry Torokhov
2018-10-29 15:23 ` Andy Shevchenko
2018-10-29 17:22 ` Rajat Jain
2018-10-29 17:43 ` Andy Shevchenko
2018-10-29 19:43 ` Rajat Jain
2018-10-29 22:17 ` [PATCH v2] " Rajat Jain
2018-10-30 7:53 ` Adrian Hunter
2018-11-12 11:05 ` Ulf Hansson
2018-11-12 11:25 ` Andy Shevchenko
2018-11-13 1:26 ` Rajat Jain
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