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. Maybe Haibo can comment on whether or not that would be an issue for the 8m[mnp] I will defer to Krzysztof and Haibo as to the proper method that we should add HS400-ES. I don't have an issue adding the imx8mn or imx8mp compatible flags to the esdhc driver if that's the decision. If that is the decision, my follow-up question would be how the YAML should look, and if it needs to change at all. adam > > > Best regards, > Krzysztof
