linux-kernel - Re: [PATCH] toshiba_acpi: Fix regression caused by backlight extra check code

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Date:	Mon, 10 Nov 2014 09:58:29 -0700
From:	Azael Avalos <coproscefalo@...il.com>
To:	Darren Hart <dvhart@...radead.org>
Cc:	rjw@...ysocki.net,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"platform-driver-x86@...r.kernel.org" 
	<platform-driver-x86@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nuno Lopes <nunoplopes@...o.pt>
Subject: Re: [PATCH] toshiba_acpi: Fix regression caused by backlight extra
 check code

Hi Darren,

Sorry for the way late reply, I had to go out of town in a hurry.

2014-11-03 23:21 GMT-07:00 Darren Hart <dvhart@...radead.org>:
> On Mon, Nov 03, 2014 at 08:58:34PM -0700, Azael Avalos wrote:
>> Bug 86521 uncovered that some TOS6208 devices also return
>> non zero values on a write call to the backlight method,
>> thus getting caught and bailed out by the extra check code.
>>
>> This patch makes sure that the extra check is being done
>> on a TOS1900 device and then make the check for the broken
>> backlight code.
>>
>> Signed-off-by: Azael Avalos <coproscefalo@...il.com>
>> ---
>>  drivers/platform/x86/toshiba_acpi.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/platform/x86/toshiba_acpi.c b/drivers/platform/x86/toshiba_acpi.c
>> index ef3a190..e3fed12 100644
>> --- a/drivers/platform/x86/toshiba_acpi.c
>> +++ b/drivers/platform/x86/toshiba_acpi.c
>> @@ -944,9 +944,13 @@ static int set_lcd_brightness(struct toshiba_acpi_dev *dev, int value)
>>       /* Extra check for "incomplete" backlight method, where the AML code
>>        * doesn't check for HCI_SET or HCI_GET and returns TOS_SUCCESS,
>>        * the actual brightness, and in some cases the max brightness.
>> +      * Use the SPFC method as an indicator that we're on a TOS1900 device,
>> +      * otherwise some TOS6208 devices might get bailed out, see bug 86521
>
> This needs a clearer description here in this comment, rather than redirecting
> the reader to a bug report (which may or may not exist when needed).

Alright, will do whenever we reach an agreement below.

>
>>        */
>> -     if (out[2] > 0  || out[3] == 0xE000)
>> -             return -ENODEV;
>> +     if (acpi_has_method(dev->acpi_dev->handle, "SPFC")) {
>
> Hrm, this checking for the existence of a specific method seems suspect to me.
> We would know if we are on a TOS1900 as we matches the acpi id already. Is the
> SPFC significant here, or is it just a "we only see SPFC on TOS1900 so it's a
> convenient test"? If the latter, it seems rather fragile and prone to other
> breakage to me.

Yeah, its the latter, the "SPFC" method is specific to TOS1900 devices.

All of the TOS1900 support the Toshiba specific backlight read-only,
and that test is just to get those implementations where the AML
code doesn't check for read/write registers, so far I've identified three
series of laptops with this issue (all Qosmios), X500, X505 and X75-A
(and there might be more around).

We could dissable backlight on all TOS1900 or add those three models
to the (growing) DMI list on video.c, but of course, I would like to keep
the code in-house, but that's just me :-)

>
> Rafael, any recommendations here?
>
>> +             if (out[2] > 0  || out[3] == 0xE000)
>> +                     return -ENODEV;
>> +     }
>>
>>       return out[0] == TOS_SUCCESS ? 0 : -EIO;
>>  }
>> --
>> 2.1.1
>>
>>
>
> --
> Darren Hart
> Intel Open Source Technology Center

Cheers
Azael



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