On Thu, 16 Jan 2020 10:50:33 +0100, Keyon Jie wrote:
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? ... }
Oh, you're right, and I completely misread the patch.
Now I took a coffee and can tell you the story behind the scene.
I believe the current code is intentionally limiting the size to the preallocated size. This limitation was brought for not trying to allocate a larger buffer when the buffer has been preallocated. In the past, most hardware allocated the continuous pages for a buffer and the allocation of a large buffer fails quite likely. This was the reason of the buffer preallocation. So, the driver wanted to tell the user-space the limit. If user needs to have an extra large buffer, they are supposed to fiddle with prealloc procfs (either setting zero to clear the preallocation or setting a large enough buffer beforehand).
For SG-buffers, though, limitation makes less sense than continuous pages. e.g. a patch below removes the limitation for SG-buffers. But changing this would definitely cause the behavior difference, and I don't know whether it's a reasonable move -- I'm afraid that apps would start hogging too much memory if the limitation is gone.
thanks,
Takashi
--- diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c index d4702cc1d376..6a6c3469bbcd 100644 --- a/sound/core/pcm_memory.c +++ b/sound/core/pcm_memory.c @@ -96,6 +96,29 @@ void snd_pcm_lib_preallocate_free_for_all(struct snd_pcm *pcm) } EXPORT_SYMBOL(snd_pcm_lib_preallocate_free_for_all);
+/* set up substream->buffer_bytes_max, which is used in hw_constraint */ +static void set_buffer_bytes_max(struct snd_pcm_substream *substream, + size_t size) +{ + substream->buffer_bytes_max = UINT_MAX; + + if (!size) + return; /* no preallocation */ + + /* for SG-buffers, no limitation is needed */ + switch (substream->dma_buffer.dev.type) { +#ifdef CONFIG_SND_DMA_SGBUF + case SNDRV_DMA_TYPE_DEV_SG: + case SNDRV_DMA_TYPE_DEV_UC_SG: +#endif + case SNDRV_DMA_TYPE_VMALLOC: + return; + } + + /* for continuous buffers, limit to the preallocated size */ + substream->buffer_bytes_max = size; +} + #ifdef CONFIG_SND_VERBOSE_PROCFS /* * read callback for prealloc proc file @@ -156,10 +179,8 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry, buffer->error = -ENOMEM; return; } - substream->buffer_bytes_max = size; - } else { - substream->buffer_bytes_max = UINT_MAX; } + set_buffer_bytes_max(substream, size); if (substream->dma_buffer.area) snd_dma_free_pages(&substream->dma_buffer); substream->dma_buffer = new_dmab; @@ -206,10 +227,8 @@ static void preallocate_pages(struct snd_pcm_substream *substream,
if (size > 0 && preallocate_dma && substream->number < maximum_substreams) preallocate_pcm_pages(substream, size); - - if (substream->dma_buffer.bytes > 0) - substream->buffer_bytes_max = substream->dma_buffer.bytes; substream->dma_max = max; + set_buffer_bytes_max(substream, substream->dma_buffer.bytes); if (max > 0) preallocate_info_init(substream); if (managed)