On 23. 08. 23 11:53, Takashi Iwai wrote:
On Wed, 23 Aug 2023 11:10:38 +0200, Jaroslav Kysela wrote:
On 23. 08. 23 10:11, Cezary Rojewski wrote:
On 2023-08-22 9:03 PM, Jaroslav Kysela wrote:
On 22. 08. 23 17:38, Takashi Iwai wrote:
On Tue, 22 Aug 2023 17:29:47 +0200, Jaroslav Kysela wrote:
On 22. 08. 23 17:07, Takashi Iwai wrote: > On Tue, 22 Aug 2023 17:03:02 +0200, > Jaroslav Kysela wrote: >> >> On 11. 08. 23 18:48, Cezary Rojewski wrote: >> >>> +#define SNDRV_PCM_SUBFMTBIT_MSBITS_32 >>> _SNDRV_PCM_SUBFMTBIT(MSBITS_32) >> >> What was reason to add 32/32 format ? Subformat STD + msbits == 32 >> should already handle the maximal resolution. Until we do not have 64 >> bit formats, it seems like an useless extension. > > My understanding is to distinguish the cases "we do fully support > 32bit" and "we don't care". But, the end effect is same for both, > user-space would handle 32bit in both cases, so this difference won't > help much, indeed.
I don't think that we have a "do not care" situation. The applications currently expects to use the maximal msbits for STD subformat. The subformat should be used only to refine (downgrade) the resolution on the driver / hw side on demand. I would just add only necessary API extensions and save one bit for now.
Well, the current behavior (with STD) is to choose whatever 32bit format the driver supports, and the driver may set a different value of hw_params.msbits at hw_params. The explicit MSBITS_32 would enforce the hw_params.msbits to be 32, otherwise hw_refine would fail. So I see a potential difference.
I see. But if our target is to create a complete query/set msbits API, we should cover all cases also for other formats.
I vote to replace SUBFMTBIT_MSBITS_32 to SUBFMTBIT_MSBITS_MAX as the second bit (right after STD). The format hw parameter already defines the maximal width. We can add SUBFMTBIT_MSBITS_32 when it's really required. Note that MAX should be handled for all cases (not only for S32_LE or so).
In my opinion STD already states "max". The word is not explicit either
- max in the eyes of whom? The driver'? Then the driver may reply: max
allowed e.g.: 24/32. And that translates to: fallback to STD.
Max in the contents of the physical sample format (S32 = 32 bits, S24 = 24 bits, S8 = 8 bits etc). It would mean, if the driver supports S32 but only with 24-bit resolution, this bit should not be set/allowed. We can also use word full or something other. If we like to extend the API in this way (force the specific msbits with the error handling), all formats should be covered. For STD - see Takashi's reply.
I think MAX can be problematic when the device supports multiple formats, say, 16bit and 32bit. Then it's not clear which MAX points to: is 16bit max or 32bit max.
I don't take this point. The subformat depends on the format, thus if one format support max, it should be set for queries.
Theoretically, this problem is in this API extension proposal too. Imagine that driver/hw support S24 and S32 formats and 20-bit msbits for one of them. How do you handle this? The subformat depends on format and should be refined when the format is known (single choice).
I find the subformat extension OK, as this doesn't need much change in API. OTOH, if we want to be more consistent way, we may extend hw_params for a new interval, e.g. SNDRV_PCM_HW_PARAM_MSBITS, and let the driver choosing it. This will need more hw_params rules and become more complex, but it allows drivers really exotic setups (like 19bit PCM :) But my gut feeling is that the subformat extension should suffice.
I'm not ok with 32 == 32. We should handle this case universally or discard.
Jaroslav