linux-kernel - Re: [PATCH v4 07/11] ASoC: jz4740-i2s: Make the PLL clock name SoC-specific

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Date:   Sat, 22 Oct 2022 21:03:53 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
Cc:     Zhou Yanjie <zhouyu@...yeetech.com>, lgirdwood@...il.com,
        broonie@...nel.org, perex@...ex.cz, tiwai@...e.com,
        linux-mips@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/11] ASoC: jz4740-i2s: Make the PLL clock name
 SoC-specific

Hi Aidan,

Le sam. 22 oct. 2022 à 18:15:05 +0100, Aidan MacDonald 
<aidanmacdonald.0x0@...il.com> a écrit :
> 
> Zhou Yanjie <zhouyu@...yeetech.com> writes:
> 
>>  Hi Paul,
>> 
>>  On 2022/7/13 下午11:07, Paul Cercueil wrote:
>>>  Hi Zhou,
>>> 
>>>  Le mer., juil. 13 2022 at 22:33:44 +0800, Zhou Yanjie 
>>> <zhouyu@...yeetech.com>
>>>  a écrit :
>>>>  Hi Aidan,
>>>> 
>>>>  On 2022/7/9 上午12:02, Aidan MacDonald wrote:
>>>>>  @@ -400,6 +402,7 @@ static const struct i2s_soc_info 
>>>>> jz4740_i2s_soc_info =
>>>>>  {
>>>>>        .field_tx_fifo_thresh    = REG_FIELD(JZ_REG_AIC_CONF, 8, 
>>>>> 11),
>>>>>        .field_i2sdiv_capture    = REG_FIELD(JZ_REG_AIC_CLK_DIV, 
>>>>> 0, 3),
>>>>>        .field_i2sdiv_playback    = REG_FIELD(JZ_REG_AIC_CLK_DIV, 
>>>>> 0, 3),
>>>>>  +    .pll_clk_name        = "pll half",
>>>>>        .shared_fifo_flush    = true,
>>>>>    };
>>>> 
>>>> 
>>>>  Since JZ4760, according to the description of the I2SCDR register,
>>>>  Ingenic SoCs no longer use PLL/2 clock, but directly use PLL 
>>>> clock,
>>>>  so it seems also inappropriate to use "pll half" for these SoCs.
>>> 
>>>  The device tree passes the clock as "pll half". So the driver 
>>> should use this
>>>  name as well...
>> 
>> 
>>  I see...
>> 
>>  It seems that the device tree of JZ4770 has used "pll half" already,
>>  but there is no "pll half" used anywhere in the device tree of 
>> JZ4780,
>>  maybe we can keep the pll_clk_name of JZ4770 as "pll half", and 
>> change
>>  the pll_clk_name of JZ4780 to a more reasonable name.
>> 
>> 
>>  Thanks and best regards!
> 
> Actually, the clock names in the DT are meaningless. The clk_get() 
> call
> matches only the clock's name in the CGU driver. So in fact the driver
> is "broken" for jz4780. It seems jz4770 doesn't work correctly either,
> it has no "pll half", and three possible parents for its "i2s" clock.

That's not true. The clock names are matched via DT.

Only in the case where a corresponding clock cannot be found via DT 
will it search for the clock name among the clock providers. I believe 
this is a legacy mechanism and you absolutely shouldn't rely on it.

-Paul

> Since the driver only supports the internal codec, which requires the
> "ext" clock, there isn't a problem in practice.
> 
> I'm just going to drop this patch and leave .set_sysclk() alone for 
> now.
> I think a better approach is to have the DT define an array of parent
> clocks for .set_sysclk()'s use, instead of hardcoding parents in the
> driver. If the parent array is missing the driver can default to using
> "ext" so existing DTs will work.
> 
> Regards,
> Aidan