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From:   Ian W MORRISON <ianwmorrison@gmail.com>
Date:   Fri, 20 Apr 2018 15:47:15 +1000
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Subject: Re: [RESEND PATCH 1/1] drm/i915/glk: Add MODULE_FIRMWARE for Geminilake
To:     Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc:     "Srivatsa, Anusha" <anusha.srivatsa@intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@intel.com>,
        "Wajdeczko, Michal" <Michal.Wajdeczko@intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        "airlied@linux.ie" <airlied@linux.ie>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
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On 18 April 2018 at 00:14, Joonas Lahtinen
<joonas.lahtinen@linux.intel.com> wrote:
> Quoting Jani Nikula (2018-04-17 12:02:52)
>> On Mon, 16 Apr 2018, "Srivatsa, Anusha" <anusha.srivatsa@intel.com> wrote:
>> >>-----Original Message-----
>> >>From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
>> >>Sent: Wednesday, April 11, 2018 5:27 AM
>> >>To: Ian W MORRISON <ianwmorrison@gmail.com>
>> >>Cc: Vivi, Rodrigo <rodrigo.vivi@intel.com>; Srivatsa, Anusha
>> >><anusha.srivatsa@intel.com>; Wajdeczko, Michal
>> >><Michal.Wajdeczko@intel.com>; Greg KH <gregkh@linuxfoundation.org>;
>> >>airlied@linux.ie; joonas.lahtinen@linux.intel.com; linux-kernel@vger.kernel.org;
>> >>stable@vger.kernel.org; intel-gfx@lists.freedesktop.org; dri-
>> >>devel@lists.freedesktop.org
>> >>Subject: Re: [RESEND PATCH 1/1] drm/i915/glk: Add MODULE_FIRMWARE for
>> >>Geminilake

<snip>

In summary so far:

Jani:
> NAK on indiscriminate Cc: stable. There are zero guarantees that
> older kernels will work with whatever firmware you throw at them.
> Who tested the firmware with v4.12 and later? We only have the CI
> results against *current* drm-tip. We don't even know about v4.16.
> I'm not going to ack and take responsibility for the stable backports
> unless someone actually comes forward with credible Tested-bys.

Anusha:
> The stable kernel version is 4.12 and beyond.
> It is appropriate to add the CC: stable in my opinion

Joonas:
> And even then, some distros will be surprised of the new MODULE_FIRMWARE
> and will need to update the linux-firmware package, too.

I've performed backport testing and some additional analysis as follows:

The DMC firmware for GLK was initially included in 4.11
  (commit: dbb28b5c3d3cb945a63030fab8d3894cf335ce19).
Then the firmware version was upgraded to 1.03 in 4.12
  (commit: f4a791819ed00a749a90387aa139706a507aa690).
However MODULE_FIRMWARE for the GLK DMC firmware
was also removed in 4.12
  (commit: d9321a03efcda867b3a8c6327e01808516f0acd7)
together with the firmware version being bumped to 1.04
  (commit: aebfd1d37194e00d4c417e7be97efeb736cd9c04).

The patch below effectively reverts commit d9321a03 because the GLK
firmware is now available in the linux-firmware repository.

To test stable backports I've used Ubuntu 18.04 (Beta 2) userspace with
both Ubuntu (generic) and self-compiled mainline (patched) kernels.
The conclusion was that the patch works across 4.12 to 4.17-rc1 kernels
additionally displaying a 'Possible missing firmware' message when
installing a kernel with the expected firmware missing.

The following are abridged backport test results:

Scenario: No DMC (glk_dmc_ver1_04.bin) firmware installed in
'/lib/firmware/i915'
  Test:Kernel installation ('grep -i dmc' output from 'apt install'):
    4.12-generic and 4.15-generic:
      No output # as expected
    4.12 to 4.17-rc1-patched:
      W: Possible missing firmware
/lib/firmware/i915/glk_dmc_ver1_04.bin for module i915
  Result: The effect of the patch is to add a 'Possible missing
firmware' message.
  Test: Booting ('grep -i dmc' output from 'dmesg'):
    4.12-generic:
      No output # as expected
    4.15-generic:
      i915 0000:00:02.0: Direct firmware load for
i915/glk_dmc_ver1_04.bin failed with error -2
      i915 0000:00:02.0: Failed to load DMC firmware
i915/glk_dmc_ver1_04.bin. Disabling runtime power management.
      i915 0000:00:02.0: DMC firmware homepage:
https://01.org/linuxgraphics/downloads/firmware
    4.12-patched:
      No output # as expected
    4.13 to 4.14-patched:
      i915 0000:00:02.0: Direct firmware load for
i915/glk_dmc_ver1_04.bin failed with error -2
      i915 0000:00:02.0: Failed to load DMC firmware
[https://01.org/linuxgraphics/downloads/firmware], disabling runtime
power management.
    4.15 to 4.17-rc1-patched:
      i915 0000:00:02.0: Direct firmware load for
i915/glk_dmc_ver1_04.bin failed with error -2
      i915 0000:00:02.0: Failed to load DMC firmware
i915/glk_dmc_ver1_04.bin. Disabling runtime power management.
      i915 0000:00:02.0: DMC firmware homepage:
https://01.org/linuxgraphics/downloads/firmware
  Result: The effect of the patch does not change existing
(non-patched kernel) messages.

Scenario: DMC (glk_dmc_ver1_04.bin) firmware installed in '/lib/firmware/i915'
  Test:Kernel installation ('grep -i dmc' output from 'apt install')
    All kernels:
      No messages # as expected
  Result: The effect of the patch does not change existing messages.
  Test" Booting ('grep -i dmc' output from 'dmesg'):
    4.12-generic:
      No output # as expected
    4.15-generic:
      i915 0000:00:02.0: Direct firmware load for
i915/glk_dmc_ver1_04.bin failed with error -2
      i915 0000:00:02.0: Failed to load DMC firmware
i915/glk_dmc_ver1_04.bin. Disabling runtime power management.
      i915 0000:00:02.0: DMC firmware homepage:
https://01.org/linuxgraphics/downloads/firmware
    4.12-patched:
      No output # as expected
    4.13 to 4.17-rc1-patched:
      [drm] Finished loading DMC firmware i915/glk_dmc_ver1_04.bin (v1.4)
  Result: The effect of the patch is to remove the 'Failed to load' message.

Regards,
Ian