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SubjectRe: [PATCH] ACPI / LPSS: Do not instiate a platform_dev for devs without a mmio resource

On 15-01-18 00:36, Rafael J. Wysocki wrote:
> On Sun, Jan 14, 2018 at 9:01 PM, Hans de Goede <> 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 <>
> 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

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.



>> ---
>> 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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