Re: [PATCH v1 10/11] ALSA: hda: cs35l41: Add device_link between HDA and cs35l41_hda

[Takashi Iwai]

On Fri, 21 Jul 2023 16:55:43 +0200,
Stefan Binding wrote:
> 
> 
> On 20/07/2023 15:21, Takashi Iwai wrote:
> > On Thu, 20 Jul 2023 15:31:46 +0200,
> > Stefan Binding wrote:
> >> To ensure consistency between the HDA core and the CS35L41 HDA
> >> driver, add a device_link between them. This ensures that the
> >> HDA core will suspend first, and resume second, meaning the
> >> amp driver will not miss any events from the playback hook from
> >> the HDA core during system suspend and resume.
> >> 
> >> Signed-off-by: Stefan Binding <sbinding@xxxxxxxxxxxxxxxxxxxxx>
> >> ---
> >>   sound/pci/hda/cs35l41_hda.c | 13 ++++++++++++-
> >>   1 file changed, 12 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/sound/pci/hda/cs35l41_hda.c b/sound/pci/hda/cs35l41_hda.c
> >> index 70aa819cfbd64..175378cdf9dfa 100644
> >> --- a/sound/pci/hda/cs35l41_hda.c
> >> +++ b/sound/pci/hda/cs35l41_hda.c
> >> @@ -1063,6 +1063,7 @@ static int cs35l41_hda_bind(struct device *dev, struct device *master, void *mas
> >>   {
> >>   	struct cs35l41_hda *cs35l41 = dev_get_drvdata(dev);
> >>   	struct hda_component *comps = master_data;
> >> +	unsigned int sleep_flags;
> >>   	int ret = 0;
> >>     	if (!comps || cs35l41->index < 0 || cs35l41->index >=
> >> HDA_MAX_COMPONENTS)
> >> @@ -1102,6 +1103,11 @@ static int cs35l41_hda_bind(struct device *dev, struct device *master, void *mas
> >>     	mutex_unlock(&cs35l41->fw_mutex);
> >>   +	sleep_flags = lock_system_sleep();
> >> +	if (!device_link_add(&comps->codec->core.dev, cs35l41->dev, DL_FLAG_STATELESS))
> >> +		dev_warn(dev, "Unable to create device link\n");
> >> +	unlock_system_sleep(sleep_flags);
> > Is lock_system_sleep() mandatory for device_link_add()?  The function
> > takes its rw lock for the race, I suppose.
> 
> I believe this is mandatory, to ensure we don't try to add the device
> link during a suspend/resume transition.
> Its probably unlikely that that would occur during the component bind,
> but just in case.

OK, it seems needed in this case.  I found the description in
device_link.rst, too.


thanks,

Takashi