Dne 05. 03. 19 v 15:23 Sven Van Asbroeck napsal(a): > Hi Takashi, > > On Mon, Mar 4, 2019 at 11:42 PM Takashi Sakamoto > <o-takashi@xxxxxxxxxxxxx> wrote: >> >> Anyway, when posting to change UAPI of Linux sound subsystem, it's >> better to describe the reason fot new stuffs; what they're designed for, >> and the reason to require them. Wnen posting in a result of series of >> discussion done previously, it's better to add any reference to it. > > My apologies for not linking in previous discussions, I'll certainly make > sure to link in the future. > > The original problem was that the fsl_ssi did not appear to work with the > tda998x hdmi codec. This codec seems to be 'unique' in the sense that it > needs to know the number of clocks per frame on the wire, i.e. the bclk_ratio, > which no-one in alsa is providing or using at the moment. > > I first made the error of conflating the physical width and the bclk_ratio, > and posted this patch - Russell King quickly pointed out my error: > https://mailman.alsa-project.org/pipermail/alsa-devel/2019-February/145916.html > > This then led to the following discussions: > https://mailman.alsa-project.org/pipermail/alsa-devel/2019-February/thread.html#145985 > https://mailman.alsa-project.org/pipermail/alsa-devel/2019-February/thread.html#145947 > > Most of the discussion is about a mechanism to convey bclk_ratio from > the frame master > to the tda998x. We don't yet seem to have a consensus on how to do this best. > > My rfc patch was only intended to provoke discussion, and to allow > people to experiment > with a flawed solution that would allow the alsa core to negotiate > bclk_ratio between > components. The uapi change is a serious flaw. bclk_ratio negotiation should be > invisible to userspace. But I cannot see a way to accomplish this. I think that this might be resolved using double constraint rules in the affected driver: snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, bclk_format_constraint, substream, SNDRV_PCM_HW_PARAM_CHANNELS, -1); snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, bclk_channels_constraint, substream, SNDRV_PCM_HW_PARAM_FORMAT, -1); And refine the format bitmask / channel interval according your bclk constraint. The physical sample width can be obtained in both bclk_format_constraint / bclk_channels_constraint function so all input values are known. The final bclk value can be obtained like in your proposed code: params_channels(params) * params_width(params) Jaroslav -- Jaroslav Kysela <perex@xxxxxxxx> Linux Sound Maintainer; ALSA Project; Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
