Re: [PATCH 3/5] arm64: dts: imx8mp: Enable HS400-ES

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Adam,

On 28.03.22 12:47, Adam Ford wrote:
> On Mon, Mar 28, 2022 at 2:20 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>>
>> Hello Adam,
>>
>> On 27.03.22 14:38, Adam Ford wrote:
>>> The SDHC controller in the imx8mp has the same controller
>>> as the imx8mm which supports HS400-ES. Change the compatible
>>> fallback to imx8mm to enable it.
>>
>> I believe that's a shortcoming of the Linux driver, which should explicitly list
>> fsl,imx8mp-usdhc in its compatibles and enable HS400-ES for it.
>>
>> I find dropping compatibles problematic, because like Linux matching
>> fsl,imx8mm-usdhc, but not fsl,imx8mp-usdhc, other software may match
>> fsl,imx7d-usdhc, but not fsl,imx8[mp]-usdhc.
>>
>> I'd prefer that either the kernel driver gains extra compatibles or that
>> the DTS lists extra compatibles and we refrain from dropping existing
>> (correct) ones.
>>
> 
> I would argue that imx7d is not correct since the IP blocks between
> imx7d and imx8mm have different flags/quirks.  One of which includes
> HS400-ES, but there are other differences as well.

The DTS currently says that an fsl,imx7d-usdhc is a subset of an
fsl,imx8mm-usdhc. So a driver could treat both HW the exact same
by focusing on the i.MX7D parts. Linux apparently did exactly
that so far. Is this not accurate?


>> What do you think?
> 
> From my understanding of the fallback compatibility strings is to
> avoid having to add more and more compatible strings to the drivers
> when they do not serve a functional purpose. Based On a conversation
> with Krzysztof [1], he suggested we update the YAML file based on the
> fallback, but he wanted NXP to give their feedback as to what the
> right fallback strings should be.  Haibo from NXP sent me a hierarchy
> [1] which is what I used to update the YAML file.  Based on the YAML
> file, the fallback in each DTSI file was updated to ensure the use of
> the proper IP block.

Myself I am in favor of moving to three compatibles instead of dropping one.
For some theoretical fsl,imx8mf-usdhc that's supposed to be exactly the same
as a fsl,imx8mm-usdhc, I don't mind omitting the fsl,imx7d-usdhc compatible,
but for existing device trees, this may introduce needless potential breakage
for other software that also uses Linux device trees.

Cheers,
Ahmad

> 
> adam
> 
> [1] - https://lore.kernel.org/linux-arm-kernel/CAHCN7xLWoUGi-jfxR2a0gvEFkPT3USUEb+8U3CCqCb5wWEJ8xw@mail.gmail.com/T/
> 
>>
>> Cheers,
>> Ahmad
>>
>>> Signed-off-by: Adam Ford <aford173@gmail.com>
>>> ---
>>>  arch/arm64/boot/dts/freescale/imx8mp.dtsi | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm64/boot/dts/freescale/imx8mp.dtsi b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
>>> index 794d75173cf5..d5ee1520f1fe 100644
>>> --- a/arch/arm64/boot/dts/freescale/imx8mp.dtsi
>>> +++ b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
>>> @@ -769,7 +769,7 @@ i2c6: i2c@30ae0000 {
>>>                       };
>>>
>>>                       usdhc1: mmc@30b40000 {
>>> -                             compatible = "fsl,imx8mp-usdhc", "fsl,imx7d-usdhc";
>>> +                             compatible = "fsl,imx8mp-usdhc", "fsl,imx8mm-usdhc";
>>>                               reg = <0x30b40000 0x10000>;
>>>                               interrupts = <GIC_SPI 22 IRQ_TYPE_LEVEL_HIGH>;
>>>                               clocks = <&clk IMX8MP_CLK_DUMMY>,
>>> @@ -783,7 +783,7 @@ usdhc1: mmc@30b40000 {
>>>                       };
>>>
>>>                       usdhc2: mmc@30b50000 {
>>> -                             compatible = "fsl,imx8mp-usdhc", "fsl,imx7d-usdhc";
>>> +                             compatible = "fsl,imx8mp-usdhc", "fsl,imx8mm-usdhc";
>>>                               reg = <0x30b50000 0x10000>;
>>>                               interrupts = <GIC_SPI 23 IRQ_TYPE_LEVEL_HIGH>;
>>>                               clocks = <&clk IMX8MP_CLK_DUMMY>,
>>> @@ -797,7 +797,7 @@ usdhc2: mmc@30b50000 {
>>>                       };
>>>
>>>                       usdhc3: mmc@30b60000 {
>>> -                             compatible = "fsl,imx8mp-usdhc", "fsl,imx7d-usdhc";
>>> +                             compatible = "fsl,imx8mp-usdhc", "fsl,imx8mm-usdhc";
>>>                               reg = <0x30b60000 0x10000>;
>>>                               interrupts = <GIC_SPI 24 IRQ_TYPE_LEVEL_HIGH>;
>>>                               clocks = <&clk IMX8MP_CLK_DUMMY>,
>>
>>
>> --
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> 


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