linux-kernel - Re: [PATCH] ACPI / LPSS: Do not instiate a platform

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Message-ID: <eaa39560-7386-4d24-756d-24ef97cb6392@redhat.com>
Date:   Mon, 15 Jan 2018 09:42:48 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI / LPSS: Do not instiate a platform_dev for devs
 without a mmio resource

Hi,

On 15-01-18 00:36, Rafael J. Wysocki wrote:
> On Sun, Jan 14, 2018 at 9:01 PM, Hans de Goede <hdegoede@...hat.com> wrote:
>> acpi_lpss_create_device() skips handling LPSS devices which do not have
>> a mmio resources in their resource list (typically these devices are
>> disabled by the firmware). But since the LPSS code does not bind to the
>> device, acpi_bus_attach() ends up still creating a platform device for
>> it and the regular platform_driver for the ACPI HID still tries to bind
>> to it.
>>
>> This happens e.g. on some boards which do not use the pwm-controller
>> and have an empty or invalid resource-table for it. Currently this causes
>> these error messages to get logged:
>> [    3.281966] pwm-lpss 80862288:00: invalid resource
>> [    3.287098] pwm-lpss: probe of 80862288:00 failed with error -22
>>
>> This commit stops the undesirable creation of a platform_device for
>> disabled LPSS devices by setting pnp.type.platform_id to 0. Note that
>> acpi_scan_attach_handler() also sets pnp.type.platform_id to 0 when there
>> is a matching handler for the device and that handler has no attach
>> callback, so we simply behave as a handler without an attach function
>> in this case.
>>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> 
> Does this fix new behavior or is it an old issue?

The problem this addresses is likely caused by the acpi_always_present
entry for the CHT 80862288 PWM devices in drivers/acpi/x86/utils.c.

The problem is that under Windows the Intel GPU driver has hardcoded
addresses for the PWM LPSS bits (or so I believe), rather then having
it as a separate device with a separate driver, so the CHT LPSS PWM
device's _STA returns 0 on all x86 devices which ship with Windows.

On most CHT laptops / tablets it is used to control the backlight
brightness so we do need the device under Linux, where we've a
separate PWM driver and we don't want to be hardcoding stuff like
this.

So we really cannot do without the acpi_always_present entry, and thus
need this extra check for devices where the pwm is actually unused
and disabled by the firmware.

Regards,

Hans

>> ---
>>   drivers/acpi/acpi_lpss.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/acpi/acpi_lpss.c b/drivers/acpi/acpi_lpss.c
>> index 9cfe6b71078b..166a8e582d96 100644
>> --- a/drivers/acpi/acpi_lpss.c
>> +++ b/drivers/acpi/acpi_lpss.c
>> @@ -610,6 +610,8 @@ static int acpi_lpss_create_device(struct acpi_device *adev,
>>          acpi_dev_free_resource_list(&resource_list);
>>
>>          if (!pdata->mmio_base) {
>> +               /* Avoid acpi_bus_attach() instantiating a pdev for this dev. */
>> +               adev->pnp.type.platform_id = 0;
>>                  /* Skip the device, but continue the namespace scan. */
>>                  ret = 0;
>>                  goto err_out;
>> --
>> 2.14.3
>>
>> --
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