On Nov 23 2017 08:44, Maciej S. Szmigiero wrote:
On 23.11.2017 00:27, Takashi Sakamoto wrote:
On Nov 23 2017 04:17, Maciej S. Szmigiero wrote:
(..)
--- a/include/uapi/sound/asound.h +++ b/include/uapi/sound/asound.h @@ -236,7 +236,11 @@ typedef int __bitwise snd_pcm_format_t; #define SNDRV_PCM_FORMAT_DSD_U32_LE ((__force snd_pcm_format_t) 50) /* DSD, 4-byte samples DSD (x32), little endian */ #define SNDRV_PCM_FORMAT_DSD_U16_BE ((__force snd_pcm_format_t) 51) /* DSD, 2-byte samples DSD (x16), big endian */ #define SNDRV_PCM_FORMAT_DSD_U32_BE ((__force snd_pcm_format_t) 52) /* DSD, 4-byte samples DSD (x32), big endian */ -#define SNDRV_PCM_FORMAT_LAST SNDRV_PCM_FORMAT_DSD_U32_BE +#define SNDRV_PCM_FORMAT_S20_4LE ((__force snd_pcm_format_t) 53) /* in four bytes */ +#define SNDRV_PCM_FORMAT_S20_4BE ((__force snd_pcm_format_t) 54) /* in four bytes */ +#define SNDRV_PCM_FORMAT_U20_4LE ((__force snd_pcm_format_t) 55) /* in four bytes */ +#define SNDRV_PCM_FORMAT_U20_4BE ((__force snd_pcm_format_t) 56) /* in four bytes */ +#define SNDRV_PCM_FORMAT_LAST SNDRV_PCM_FORMAT_U20_4BE
In my opinion, for this type of definition, it's better to declare left/right-adjusted or padding side. (Of course, silence definition is already a hint, however the lack of information forces developers to have a careful behaviour to handle entries on the list. (I note that in current ALSA PCM interface there's no way to deliver MSB/LSB-first information about sample format.)
No other sound format includes this information in its name
You overlook comments in 'SNDRV_PCM_FORMAT_[U|S]24_[LE|BE]'. Let me refer to them [1]:
198 #define SNDRV_PCM_FORMAT_S24_LE ((__force snd_pcm_format_t) 6) /* low three bytes */ 199 #define SNDRV_PCM_FORMAT_S24_BE ((__force snd_pcm_format_t) 7) /* low three bytes */ 200 #define SNDRV_PCM_FORMAT_U24_LE ((__force snd_pcm_format_t) 8) /* low three bytes */ 201 #define SNDRV_PCM_FORMAT_U24_BE ((__force snd_pcm_format_t) 9) /* low three bytes */
In your way, these types of format can be represented by 'SNDRV_PCM_FORMAT_[U|S]24_4[LE|BE]', thus for playback direction they mean:
``` #include <sound/asound.h> #include <endian.h>
uint32_t *buf; uint32_t sample; snd_pcm_format_t format;
sample = generate_a_sample(); (sample & ~0x00ffffff) /* invalid bits as sample */
if (format == SNDRV_PCM_FORMAT_[U|S]24_LE) { buf[0] = htole32(sample); else buf[0] = htobe32(sample);
/* transfer content of the buf via ALSA kernel stuffs. */ ```
The comments are good enough for application developers in an aspect of a position for padding.
In general, studying from the past is preferable behaviour to be genius, however accumulated history includes mistakes and defects. Just pretending the past is not so genius, without further consideration.
Actually additions of the rest of entries for PCM format were done without enough cares of what information they give to application developers. Adding new entries is easier than fixing and improving them once exposed. It's a reason that they're left what they're.
I wish you had enough care to assist applications developers. Without applications, drivers are worthless and just waste of code base.
so if we name these formats SNDRV_PCM_FORMAT_{S, U}20LSB_4 they are going to have it inconsistent with every other one
(I assume you meant to include such information in a format name?).
But information about whether this format is MSB or LSB justified can be added in a comment so the situation is clear for other developers from the definition without needing to read the actual processing code.
For consistency of the other entries, this is not so preferable, in my opinion. So I didn't suggest it and just noted.
Additionally, alsa-lib includes some codes related to the definition[1]. If you'd like to thing goes well out of ALSA SoC part, it's better to submit changes to the library as well.
[1] http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm_misc.c;h=54...
I have alsa-lib changes ready for these formats - they were needed to test these patches, will post them when this is merged on the kernel side (in case some changes are needed which affect both).
Please pay enough care when writing patch comment. Silence means nothing, at least for reviewers, even if you have good preparations.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/tree/include...
Regards
Takashi Sakamoto