Re: [RFC PATCH v1 22/57] sound: Remove PAGE_SIZE compile-time constant assumption

Ryan Roberts
2024-10-14T13:42:25Z

On 14/10/2024 13:41, Takashi Iwai wrote:
> On Mon, 14 Oct 2024 14:24:02 +0200,
> Ryan Roberts wrote:
>>
>> On 14/10/2024 12:38, Mark Brown wrote:
>>> On Mon, Oct 14, 2024 at 11:58:29AM +0100, Ryan Roberts wrote:
>>>> -static const struct snd_pcm_hardware dummy_dma_hardware = {
>>>> +static DEFINE_GLOBAL_PAGE_SIZE_VAR_CONST(struct snd_pcm_hardware, dummy_dma_hardware, {
>>>> /* Random values to keep userspace happy when checking constraints */
>>>> .info = SNDRV_PCM_INFO_INTERLEAVED |
>>>> SNDRV_PCM_INFO_BLOCK_TRANSFER,
>>>> @@ -107,7 +107,7 @@ static const struct snd_pcm_hardware dummy_dma_hardware = {
>>>> .period_bytes_max = PAGE_SIZE*2,
>>>> .periods_min = 2,
>>>> .periods_max = 128,
>>>> -};
>>>> +});
>>>
>>> It's probably better to just use PAGE_SIZE_MAX here and avoid the
>>> deferred patching, like the comment says we don't particularly care what
>>> the value actually is here given that it's a dummy.
>>
>> OK, so would that be:
>>
>> .buffer_bytes_max = 128*1024,
>> .period_bytes_min = PAGE_SIZE_MAX, <<<<<
>> .period_bytes_max = PAGE_SIZE_MAX*2, <<<<<
>> .periods_min = 2,
>> .periods_max = 128,
>>
>> ?
>>
>> It's not really clear to me how all the parameters interact; the buffer size
>> 128K, which, if PAGE_SIZE_MAX is 64K, would hold 1 period of the maximum size.
>> But periods_min is 2. So not sure that works? Or perhaps I'm trying to apply too
>> much meaning to the param names...
>
> Right, when PAGE_SIZE_MAX is 64k, 128k won't be used because of the
> constrant of periods_min=2.
>
> As Mark mentioned, here the actual size itself doesn't matter much.
> So I suppose it'd be even simpler to define just 4096 and 4096 * 2 for
> period_bytes_min and *_max instead of sticking with PAGE_SIZE. Then
> it would become platform-agnostic, too.

OK great I'll set these to 4096 and 4096*2 for the next version.

Thanks for the feedback!

>
>
> thanks,
>
> Takashi