On Thu, 2020-01-16 at 08:15 +0100, Takashi Iwai wrote:
On Thu, 16 Jan 2020 05:53:18 +0100, Keyon Jie wrote:
With today's code, we preallocate DMA buffer for substreams at pcm_new() stage, and the substream->buffer_bytes_max and substream->dma_max will save as the actually preallocated buffer size and maximum size that the dma buffer can be expanded by at hw_params() state, correspondingly.
No, it's other way round: the former, buffer_bytes_max, is the max size defined by the driver (i.e. passed in snd_pcm_hardware) and the latter, dma_max, is the max preallocation size (passed to preallocation helper).
Hi Takashi, thanks for your comment.
First of all, have you ever hit issue I mentioned in the commit message that we can't set buffer_bytes larger than the preallocated dma bytes?
I found this issue in kinds of platforms, not only on SOF/SoC ones, but also on legacy HDA ones.
Secondly, I am not clear about the design intention of the substream-
buffer_bytes_max and substream->dma_max, if it is as you commented
above, can you help answer my questions below inline the code?
void snd_pcm_lib_preallocate_pages(struct snd_pcm_substream *substream, int type, struct device *data, size_t size, size_t max)
static void preallocate_pages(struct snd_pcm_substream *substream, int type, struct device *data, size_t size, size_t max, bool managed) { ... if (substream->dma_buffer.bytes > 0) substream->buffer_bytes_max = substream-
dma_buffer.bytes;//Keyon: this is the actual allocated buffer bytes,
what is the intention here and why it is assigned to buffer_bytes_max which will be used to constrain on the _HW_PARAM_BUFFER_BYTES later?
substream->dma_max = max; //Keyon: looks here it is where the *max* param used only if we don't define SND_VERBOSE_PROCFS? what relationship can we have with the preallocation itself? ... }
At pcm_open() stage, the maximum constraint of HW_PARAM_BUFFER_BYTES is set to substream->buffer_bytes_max and returned to user space as the max interval of the HW_PARAM_BUFFER_BYTES, this will lead to issue that user can't choose any buffer-bytes larger than the preallocated buffer size, and the buffer reallocation will never happen actually.
Here change to use substream->dma_max as the maximum constraint of the HW_PARAM_BUFFER_BYTES and fix the issue mentioned above.
I don't think the logic in the current code you're changing is wrong. If there is any, it must be something else.
This might be rather the FIXME code found in snd_pcm_hw_constraints_complete()?
I just tried removing the FIXME part code and it doesn't help, the rule snd_pcm_hw_rule_buffer_bytes_max here limit the max of the SNDRV_PCM_HW_PARAM_BUFFER_BYTES and this will returned to user space like aplay for the subsequent hw_params(), is this intentional?
int snd_pcm_hw_constraints_complete(struct snd_pcm_substream *substream) { ... err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_BUFFER_BYTES, snd_pcm_hw_rule_buffer_bytes_max, substream, SNDRV_PCM_HW_PARAM_BUFFER_BYTES, -1); if (err < 0) return err;
/* FIXME: remove */ if (runtime->dma_bytes) { err = snd_pcm_hw_constraint_minmax(runtime, SNDRV_PCM_HW_PARAM_BUFFER_BYTES, 0, runtime->dma_bytes); if (err < 0) return err; }
... return 0; }
Thanks, ~Keyon