linux-kernel - Re: [PATCH v7 4/8] firmware: Add new platform fallback mechanism and firmware_request

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Message-ID: <c75ceb3a-799a-378a-dbff-c4c4f57575b4@redhat.com>
Date:   Sat, 5 Oct 2019 11:53:34 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Jonathan Corbet <corbet@....net>,
        Peter Jones <pjones@...hat.com>,
        Dave Olsthoorn <dave@...aar.me>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-input@...r.kernel.org
Subject: Re: [PATCH v7 4/8] firmware: Add new platform fallback mechanism and
 firmware_request_platform()

Hi Dmitry,

On 05-10-2019 01:17, Dmitry Torokhov wrote:
> Hi Hans,
> 
> On Fri, Oct 04, 2019 at 04:50:52PM +0200, Hans de Goede wrote:
>> In some cases the platform's main firmware (e.g. the UEFI fw) may contain
>> an embedded copy of device firmware which needs to be (re)loaded into the
>> peripheral. Normally such firmware would be part of linux-firmware, but in
>> some cases this is not feasible, for 2 reasons:
>>
>> 1) The firmware is customized for a specific use-case of the chipset / use
>> with a specific hardware model, so we cannot have a single firmware file
>> for the chipset. E.g. touchscreen controller firmwares are compiled
>> specifically for the hardware model they are used with, as they are
>> calibrated for a specific model digitizer.
>>
>> 2) Despite repeated attempts we have failed to get permission to
>> redistribute the firmware. This is especially a problem with customized
>> firmwares, these get created by the chip vendor for a specific ODM and the
>> copyright may partially belong with the ODM, so the chip vendor cannot
>> give a blanket permission to distribute these.
>>
>> This commit adds a new platform fallback mechanism to the firmware loader
>> which will try to lookup a device fw copy embedded in the platform's main
>> firmware if direct filesystem lookup fails.
>>
>> Drivers which need such embedded fw copies can enable this fallback
>> mechanism by using the new firmware_request_platform() function.
> 
> Why would drivers not want to fetch firmware from system firmware if it
> is not present on disk? I would say let driver to opt-out of this
> fallback, but default request_firmware() should do it by default.

Only few devices / device-drivers have / need firmware which is
embedded in the system-fw. Checking for this introduces an extra call
in the firmware-loader path and the firmware-loader maintainer have
requested to make this opt-in, rather then opt-out, so that these changes
do not impact the many many other drivers which do not need this.

To be precise so far only the 2 touchscreen drivers for which patches
are in this series are known to benefit from this approach. So since this
is somewhat of a special case opt-in makes more sense then opt-out.

Regards,

Hans