linux-kernel - Re: [PATCH 4/4] ALSA: pcm_dmaengine: Correct support for 3 physical bytes samples

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Date:	Wed, 2 Jul 2014 15:56:15 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Lars-Peter Clausen <lars@...afoo.de>, <vinod.koul@...el.com>,
	<dan.j.williams@...el.com>, <tiwai@...e.de>,
	Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>, <joelf@...com>,
	<nsekhar@...com>
CC:	<linux-kernel@...r.kernel.org>, <alsa-devel@...a-project.org>,
	<dmaengine@...r.kernel.org>
Subject: Re: [PATCH 4/4] ALSA: pcm_dmaengine: Correct support for 3 physical
 bytes samples

On 07/02/2014 03:48 PM, Lars-Peter Clausen wrote:
>> per discussion over the irc with Lars we could extend the masking to other
>> widths as well, which would look something like this:
>> u32 addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
>>           BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
>>           BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
>> ...
>> /*
>>   * Prepare formats mask for valid/allowed sample types. If the dma does
>>   * not have support for the given physical word size, it needs to be
>>   * masked out so user space can not use the format which produces
>>   * corrupted audio.
>>   * In case the dma driver does not implement the slave_caps the default
>>   * assumption is that it supports 1, 2 and 4 bytes widths.
>>   */
>> if (!dma_get_slave_caps(prtd->dma_chan, &dma_caps)) {
>>     if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>>         addr_widths = dma_caps.dstn_addr_widths;
>>     else
>>         addr_widths = dma_caps.src_addr_widths;
>> }
>>
>> for (i = 0; i <= SNDRV_PCM_FORMAT_LAST; i++) {
>>     int bits = snd_pcm_format_physical_width(i);
>>
>>     switch (bits) {
>>     case 8:
>>         if (!(addr_widths & BIT(DMA_SLAVE_BUSWIDTH_1_BYTE)))
>>             fmt_mask |= (1LL << i);
>>         break;
>>     case 16:
>>         if (!(addr_widths & BIT(DMA_SLAVE_BUSWIDTH_2_BYTES)))
>>             fmt_mask |= (1LL << i);
>>         break;
>>     case 24:
>>         if (!(addr_widths & BIT(DMA_SLAVE_BUSWIDTH_3_BYTES)))
>>             fmt_mask |= (1LL << i);
>>         break;
>>     case 32:
>>         if (!(addr_widths & BIT(DMA_SLAVE_BUSWIDTH_4_BYTES)))
>>             fmt_mask |= (1LL << i);
>>         break;
>>     case 64:
>>         if (!(addr_widths & BIT(DMA_SLAVE_BUSWIDTH_8_BYTES)))
>>             fmt_mask |= (1LL << i);
>>         break;
>>     default:
>>         fmt_mask |= (1LL << i);
>>         break;
>>     }
>> }
>>
>> Is this sounds better?
> 
> Sounds good. I think we can assume that DMA_SLAVE_BUSWIDTH_1_BYTE = 1, ...
> So (addr_width & BIT(bits / 8)) should work fine and we do not need to
> duplicate the case branches.
> 
> The other thing is this should go into dmaengine_pcm_set_runtime_hwparams()
> where we also restrict the other hardware parameters based on the dmaengine
> capabilities.

true

-- 
Péter
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