On 28/03/2022 15:07, Ahmad Fatoum wrote: > Hello Krzysztof, > > On 28.03.22 14:56, Krzysztof Kozlowski wrote: >> On 28/03/2022 14:45, Adam Ford wrote: >>> On Mon, Mar 28, 2022 at 6:49 AM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: >>>> >>>> On 28/03/2022 13:09, Ahmad Fatoum wrote: >>>>> Hello Adam, >>>>> >>>>> On 28.03.22 12:47, Adam Ford wrote: >>>>>> On Mon, Mar 28, 2022 at 2:20 AM Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> 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. >>>>> >>>> >>>> Affecting existing users is indeed a concern with this approach, because >>>> in-kernel DTS might be used in other projects as well. >>>> >>>> I still cannot find here the answer whether fsl,imx8mm-usdhc is actually >>>> compatible with fsl,imx7d-usdhc. It's not about driver, but about >>>> hardware and programming model. imx8mm can support additional features >>>> and still be compatible with imx7d. However if any flags of imx7d are >>>> actually not valid for imx8mm, then it's different case. >>> >>> The imx7d flags are: >>> ESDHC_FLAG_USDHC >>> ESDHC_FLAG_STD_TUNING >>> ESDHC_FLAG_HAVE_CAP1 >>> ESDHC_FLAG_HS200 >>> ESDHC_FLAG_HS400 >>> ESDHC_FLAG_STATE_LOST_IN_LPMODE >>> ESDHC_FLAG_BROKEN_AUTO_CMD23, >>> >>> The imx8mm flags are: >>> ESDHC_FLAG_USDHC >>> ESDHC_FLAG_STD_TUNING >>> ESDHC_FLAG_HAVE_CAP1 >>> ESDHC_FLAG_HS200 >>> ESDHC_FLAG_HS400 >>> ESDHC_FLAG_HS400_ES >>> ESDHC_FLAG_STATE_LOST_IN_LPMODE >>> >>> It does not have the ESDHC_FLAG_BROKEN_AUTO_CMD23 that is present in the imx7d. >> >> AFAIU, it looks imx8mm is compatible with imx7d, because the broken >> acmd23 only limits the features. If imx8mm binds according to imx7d, it >> will not support acmd23 and HS400-ES. >> >> Having three compatibles is therefore also OK. > > My thoughts, exactly. > >> You could also add two cases: >> 1. three compatibles, deprecated: True, >> 2. two compatibles, without imx7d. >> >> Existing DTS stays with three compatibles for two years and later gets >> converted to two compatibles. New DTS should use two compatibles. >> >> It's quite a lot of churn, but would make in the long term bindings >> correct and also not break other users/projects. > > I don't see why we need to deprecate the old binding. New SoCs > can be imx8mm-usdhc compatible from the beginning and need not > care about the old binding. Existing SoCs can just remain imx7d-usdhc > compatible as they are now. > > I don't see what the deprecation accomplishes. It avoids to have too many entries of imx8mm (imx8mm alone, imx8mm+imx7d, imx8xx+imx8mm+imx7d). Best regards, Krzysztof
