linux-kernel - Re: [PATCH 1/2] ALSA: pcm: add SNDRV_PCM_FORMAT_{S, U}20

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Date:   Thu, 23 Nov 2017 00:44:19 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Takashi Sakamoto <o-takashi@...amocchi.jp>
Cc:     Timur Tabi <timur@...i.org>, Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] ALSA: pcm: add SNDRV_PCM_FORMAT_{S, U}20_4

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 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.

> 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=5420b1895713a3aec3624a5218794a7b49baf167;hb=HEAD

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).

> Regards
> 
> Takashi Sakamoto

Best regards,
Maciej Szmigiero