linux-kernel - Re: [PATCH v6 10/10] ASoC: rockchip

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 15 Oct 2015 10:53:36 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Shawn Lin <shawn.lin@...k-chips.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>, Mark Brown <broonie@...nel.org>
CC:	Doug Anderson <dianders@...omium.org>,
	Olof Johansson <olof@...om.net>,
	Sonny Rao <sonnyrao@...omium.org>,
	Addy Ke <addy.ke@...k-chips.com>,
	Boojin Kim <boojin.kim@...sung.com>, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, alsa-devel@...a-project.org,
	linux-spi@...r.kernel.org, Yiwei Cai <cain.cai@...k-chips.com>,
	Jianqun Xu <xjq@...k-chips.com>
Subject: Re: [PATCH v6 10/10] ASoC: rockchip_i2s: modify DMA max burst to
 1

On 10/15/2015 03:36 AM, Shawn Lin wrote:
[...]
> +
> +	if (snd_dmaengine_pcm_get_caps(&pdev->dev, &dma_caps) == 0) {
> +		if (dma_caps.max_burst > 4) {
> +			i2s->playback_dma_data.maxburst = 4;
> +			i2s->capture_dma_data.maxburst = 4;
> +		} else {
> +			i2s->playback_dma_data.maxburst = 1;
> +			i2s->capture_dma_data.maxburst = 1;

So this is what this is all about? I though you might have to program some
FIFO threshold registers in the peripheral itself.

But it seems all this does is to read the maximum burst length from the DMA
controller only to tell the DMA controller that this is the maximum burst
length it should use. That seems rather unnecessary.

The maxburst field of the dma_data indicates the maximum burst length that
the audio peripheral can handle. Typically this is the number of samples the
audio FIFO can receive without overflowing after sending the DMA request
signal. Since as the name suggests this is the maximum burst size the DMA
controller is free to choose a burst size smaller than this when writing
data to the peripheral.

So in your case instead of introducing all these facilities to query the
maximum burst size it should be OK to simply reduce the burst size in the
DMA controller itself when it gets a request with a burst size larger than
it can handle, or is there a reason why this is not possible?

- Lars
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/