Re: [PATCH 2/3] ALSA: emu10k1: remove superfluous IRQ enable state saving

[Oswald Buddenhagen <oswald.buddenhagen@gmx.de>]

On Thu, Jul 13, 2023 at 07:55:31AM +0200, Takashi Iwai wrote:
>On Wed, 12 Jul 2023 16:57:49 +0200,
>Oswald Buddenhagen wrote:
>> 
>> The mixer, PCM prepare, MIDI, synth driver, and procfs callbacks are all
>> always invoked with IRQs enabled, so there is no point in saving the
>> state.
>> 
>> snd_emu1010_load_firmware_entry() is called from emu1010_firmware_work()
>> and snd_emu10k1_emu1010_init(); the latter from snd_emu10k1_create() and
>> snd_emu10k1_resume(), all of which have IRQs enabled.
>> 
>> The voice and memory functions are called from mixed contexts, so they
>> keep the state saving.
>> 
>> The low-level functions all keep the state saving, because it's not
>> feasible to keep track of what is called where.
>> 
>Wouldn't it make more sense if you replace it with a mutex?
>It'll become more obvious that it's only for non-IRQ context, too.
>
huh?
at least some of the ~six different locks touched by this patch 
absolutely _are_ used in irq context. this patch is concerned only about 
the specific call sites, where we know that local irqs are enabled, so 
we can unconditionally re-enable them rather than restoring the old 
state (the latter being a much more expensive operation). the code 
already contains precedents for this, and the complementary optimization 
of not disabling/restoring irqs where we know that they are already 
disabled.

the reg_lock would be convertible to a mixer_mutex in most mixer 
callbacks, but that is an orthogonal question, which is raised in the 
next commit.

regards