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SubjectRe: [PATCH 20/25] ASoC: sun8i-codec: Protect the clock rate while streams are open
On Mon, Oct 05, 2020 at 11:43:51PM -0500, Samuel Holland wrote:
> On 10/5/20 7:01 AM, Maxime Ripard wrote:
> > On Wed, Sep 30, 2020 at 09:11:43PM -0500, Samuel Holland wrote:
> >> The codec's clock input is shared among all AIFs, and shared with other
> >> audio-related hardware in the SoC, including I2S and SPDIF controllers.
> >> To ensure sample rates selected by userspace or by codec2codec DAI links
> >> are maintained, the clock rate must be protected while it is in use.
> >>
> >> Signed-off-by: Samuel Holland <samuel@sholland.org>
> >> ---
> >> sound/soc/sunxi/sun8i-codec.c | 25 ++++++++++++++++++++++---
> >> 1 file changed, 22 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/sound/soc/sunxi/sun8i-codec.c b/sound/soc/sunxi/sun8i-codec.c
> >> index 501af64d43a0..86065bee7cd3 100644
> >> --- a/sound/soc/sunxi/sun8i-codec.c
> >> +++ b/sound/soc/sunxi/sun8i-codec.c
> >> @@ -416,27 +416,32 @@ static int sun8i_codec_get_lrck_div_order(unsigned int slots,
> >> unsigned int div = slots * slot_width;
> >>
> >> if (div < 16 || div > 256)
> >> return -EINVAL;
> >>
> >> return order_base_2(div);
> >> }
> >>
> >> +static unsigned int sun8i_codec_get_sysclk_rate(unsigned int sample_rate)
> >> +{
> >> + return sample_rate % 4000 ? 22579200 : 24576000;
> >> +}
> >> +
> >> static int sun8i_codec_hw_params(struct snd_pcm_substream *substream,
> >> struct snd_pcm_hw_params *params,
> >> struct snd_soc_dai *dai)
> >> {
> >> struct sun8i_codec *scodec = snd_soc_dai_get_drvdata(dai);
> >> struct sun8i_codec_aif *aif = &scodec->aifs[dai->id];
> >> unsigned int sample_rate = params_rate(params);
> >> unsigned int slots = aif->slots ?: params_channels(params);
> >> unsigned int slot_width = aif->slot_width ?: params_width(params);
> >> - unsigned int sysclk_rate = clk_get_rate(scodec->clk_module);
> >> - int lrck_div_order, word_size;
> >> + unsigned int sysclk_rate = sun8i_codec_get_sysclk_rate(sample_rate);
> >> + int lrck_div_order, ret, word_size;
> >> u8 bclk_div;
> >>
> >> /* word size */
> >> switch (params_width(params)) {
> >> case 8:
> >> word_size = 0x0;
> >> break;
> >> case 16:
> >> @@ -466,17 +471,30 @@ static int sun8i_codec_hw_params(struct snd_pcm_substream *substream,
> >> (lrck_div_order - 4) << SUN8I_AIF1CLK_CTRL_AIF1_LRCK_DIV);
> >>
> >> /* BCLK divider (SYSCLK/BCLK ratio) */
> >> bclk_div = sun8i_codec_get_bclk_div(sysclk_rate, lrck_div_order, sample_rate);
> >> regmap_update_bits(scodec->regmap, SUN8I_AIF1CLK_CTRL,
> >> SUN8I_AIF1CLK_CTRL_AIF1_BCLK_DIV_MASK,
> >> bclk_div << SUN8I_AIF1CLK_CTRL_AIF1_BCLK_DIV);
> >>
> >> - if (!aif->open_streams) {
> >> + /* SYSCLK rate */
> >> + if (aif->open_streams) {
> >> + ret = clk_set_rate(scodec->clk_module, sysclk_rate);
> >> + if (ret < 0)
> >> + return ret;
> >> + } else {
> >> + ret = clk_set_rate_exclusive(scodec->clk_module, sysclk_rate);
> >
> > It's not really clear to me why we wouldn't want to always protect the
> > clock rate here?
>
> From Documentation/sound/kernel-api/writing-an-alsa-driver.rst:
>
> hw_params callback
> ...
> Note that this and ``prepare`` callbacks may be called multiple
> times per initialization. For example, the OSS emulation may call
> these callbacks at each change via its ioctl.
>
> Clock rate protection is reference counted, so we must only take one
> reference (or at least a known number of references) per stream.

Ah, right.

Can you add a comment to make that more obvious?

> >> + if (ret == -EBUSY)
> >> + dev_err(dai->dev, "%s: clock is busy! Sample rate %u Hz "
> >> + "conflicts with other audio streams.\n",
> >
> > This string creates a checkpatch warning.
>
> I will put it on one line, though >100 columns is also a checkpatch warning.

Yeah, but in general having an error on a single line is more important.
That way you can then grep for that error message

Maxime
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