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

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Message-ID: <d75c1902-b715-4a33-1965-ec06d625e3ac@linux.intel.com>
Date:   Mon, 24 Jul 2023 12:25:19 +0200
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...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.



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?


>> +
>>  	for_each_pci_dev(display_dev) {
>>  		if (display_dev->vendor == PCI_VENDOR_ID_INTEL &&
>>  		    (display_dev->class >> 16) == PCI_BASE_CLASS_DISPLAY &&
>