linux-kernel - Re: [PATCH v2 2/9] ALSA: hda/i915: Allow override of gpu binding.

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Message-ID: <932c4293-375f-685c-2cfd-0bc80fd80683@linux.intel.com>
Date:   Tue, 25 Jul 2023 11:54:41 +0200
From:   Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        alsa-devel@...a-project.org
Cc:     sound-open-firmware@...a-project.org, linux-kernel@...r.kernel.org,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Daniel Baluta <daniel.baluta@....com>
Subject: Re: [PATCH v2 2/9] ALSA: hda/i915: Allow override of gpu binding.

Hey,

On 2023-07-24 12:25, Pierre-Louis Bossart wrote:
> 
> 
> On 7/21/23 14:19, Péter Ujfalusi wrote:
>>
>>
>> On 19/07/2023 19:41, Maarten Lankhorst wrote:
>>> Selecting CONFIG_DRM selects CONFIG_VIDEO_NOMODESET, which exports
>>> video_firmware_drivers_only(). This can be used as a first
>>> approximation on whether i915 will be available. It's safe to use as
>>> this is only built when CONFIG_SND_HDA_I915 is selected by CONFIG_I915.
>>>
>>> It's not completely fool proof, as you can boot with "nomodeset
>>> i915.modeset=1" to make i915 load regardless, or use
>>> "i915.force_probe=!*" to never load i915, but the common case of
>>> booting with nomodeset to disable all GPU drivers this will work as
>>> intended.
>>>
>>> Because of this, we add an extra module parameter,
>>> snd_hda_core.gpu_bind that can be used to signal users intent.
>>> -1 follows nomodeset, 0 disables binding, 1 forces wait/-EPROBE_DEFER
>>> on binding.
>>
>> Reviewed-by: Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>
>>
>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
>>> ---
>>>   sound/hda/hdac_i915.c | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>>>
>>> diff --git a/sound/hda/hdac_i915.c b/sound/hda/hdac_i915.c
>>> index 161a9711cd63e..c32709fa4115f 100644
>>> --- a/sound/hda/hdac_i915.c
>>> +++ b/sound/hda/hdac_i915.c
>>> @@ -11,6 +11,13 @@
>>>   #include <sound/hda_i915.h>
>>>   #include <sound/hda_register.h>
>>>   
>>> +#include <video/nomodeset.h>
>>> +
>>> +static int gpu_bind = -1;
>>> +module_param(gpu_bind, int, 0644);
>>> +MODULE_PARM_DESC(gpu_bind, "Whether to bind sound component to GPU "
>>> +			   "(1=always, 0=never, -1=on nomodeset(default))");
>>> +
>>>   #define IS_HSW_CONTROLLER(pci) (((pci)->device == 0x0a0c) || \
>>>   				((pci)->device == 0x0c0c) || \
>>>   				((pci)->device == 0x0d0c) || \
>>> @@ -121,6 +128,9 @@ static int i915_gfx_present(struct pci_dev *hdac_pci)
>>>   {
>>>   	struct pci_dev *display_dev = NULL;
>>>   
>>> +	if (!gpu_bind || (gpu_bind < 0 && video_firmware_drivers_only()))
>>> +		return false;
> 
> 
> Bear with me since I am just going back to work mode but I can't figure
> out what the second part of the test does
> 
> bool video_firmware_drivers_only(void)
> {
> 	return video_nomodeset;
> }
> EXPORT_SYMBOL(video_firmware_drivers_only);
> 
> and video_nomodeset=1 by default, so why would we return false when
> gpu_bind = -1?
> 
> This seems to be a change of functionality, what am I missing?
video_nomodeset is 0 by default, only when nomodeset is given as 
argument is it set to 1. :-)

Cheers,
~Maarten