Dne 12. 10. 20 v 15:55 Vinod Koul napsal(a): > On 12-10-20, 15:29, Jaroslav Kysela wrote: >> Dne 12. 10. 20 v 14:24 Vinod Koul napsal(a): >>> On 12-10-20, 09:01, Takashi Iwai wrote: >>>> On Mon, 12 Oct 2020 07:25:25 +0200, >>> >>>>> So what if we add another state but keep it in kernel (hidden from >>>>> userspace)...? >>>> >>>> That's fine, then it's just a kernel's business, and it should be >>>> determined which one makes the code better. >>>> >>>> But, there are things to be considered, though: >>>> >>>> - SNDRV_PCM_STATE_* is defined as snd_pcm_state_t with __bitwise. >>>> This indicates that the type has to be defined in that way >>>> explicitly. >>>> >>>> - Having a value over SNDRV_PCM_STATE_LAST internally is hackish. >>>> >>>>> Right now tinycompress does not make use of PCM streams, kernel handles >>>>> these. I am not aware of any other implementation. >>>>> >>>>> So if the scope if within compress then it might work... >>>> >>>> Yes. But currently the API uses SND_PCM_* even for the compress >>>> stuff. Changing this value means to have influence on PCM, even if >>>> PCM stuff doesn't use it yet. (At least you'd need to increase >>>> SND_PCM_STATE_LAST, for example.) >>>> >>>> That said, if we want to change only for compress API by assuming that >>>> the impact must be negligible, the first step would be to move from >>>> SND_PCM_STATE_* to the own state, SND_COMPRESS_STATE_*. The values >>>> should be compatible, but this has to be changed at first. Then you >>>> can introduce a new value there. >>> >>> I think that sounds reasonable to me, we should not have used >>> SNDRV_PCM_STATE_* in the first place and long term fix for this should >>> be SNDRV_COMPRESS_STATE_ >>> >>> I will cook a patch for this >> >> Although the impact is not high, I do think that we should enable the new >> behaviour conditionally (when the user space asks for it) even if the state >> values are split. I think that the whole thread is about 'how to extend the >> current APIs'. The hidden way is really not so nice. >> >> Unfortunately, there are no reserved fields in the snd_compr_params structure >> for this, but I see the similarity with the 'no_wake_mode' field which >> controls the driver behaviour. > > I was not really thinking of exporting the states to userspace. > Tinycompress does not use it, I do not see any uses of it to enable > userspace with it.. Do you think it should be exposed? If so why..? I don't think that it's required to expose the state for the compressed API to add this new feature. I just talk about to activate the new feature conditionally. The question is how to extend the API now. > Worst case we add an ioctl to query the state.. the state transitions > are anyway result of control ops on the stream > > Btw what was the motivation for pcm to expose the stream states..? The driver may change the state when underrun / overrun or an I/O error occurs and there's also mmap write/read mode, so the traditional read/write with an error code handling does not work here. Also, the user space should know the state anyway, so it's better to have all parts synced. Jaroslav -- Jaroslav Kysela <perex@xxxxxxxx> Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
