linux-kernel - Re: [RFC PATCH 10/34] ASoC: sun8i-codec: Advertise only hardware-supported rates

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Date:   Mon, 17 Feb 2020 19:55:03 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 10/34] ASoC: sun8i-codec: Advertise only
 hardware-supported rates

On 2/17/20 9:30 AM, Mark Brown wrote:
> On Mon, Feb 17, 2020 at 12:42:26AM -0600, Samuel Holland wrote:
>> The hardware does not support 64kHz, 88.2kHz, or 176.4kHz sample rates,
>> so the driver should not advertise them. The hardware can handle two
>> additional non-standard sample rates: 12kHz and 24kHz, so declare
>> support for them via SNDRV_PCM_RATE_KNOT.
>>
>> Cc: stable@...nel.org
>> Fixes: 36c684936fae ("ASoC: Add sun8i digital audio codec")
>> Fixes: eda85d1fee05 ("ASoC: sun8i-codec: Add ADC support for a33")
>> Signed-off-by: Samuel Holland <samuel@...lland.org>
> 
> The new sample rates are new functionality, they are definitely not
> stable material.   For the sample rates you are removing do we
> understand why they were added - do they work for people, are they
> perhaps supported for some users and not others for example?

I do not know why they were added, but the sample rates I removed do not work
today, for anyone.

The sample rate must be programmed into the hardware, and the removed sample
rates do not map to one of the possible register values, so
sun8i_codec_get_hw_rate(), and thus hw_params, will return -EINVAL if one of
them is used.