Re: [PATCH v1 0/1] tegra_mmc: get tap and trim from dts

[Thierry Reding <thierry.reding@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2005 bytes --]

On Wed, Aug 23, 2023 at 02:30:48PM +0300, Svyatoslav Ryhel wrote:
> 
> 
> 23 серпня 2023 р. 13:53:26 GMT+03:00, Thierry Reding <thierry.reding@gmail.com> написав(-ла):
> >On Sat, Aug 19, 2023 at 06:35:00PM +0300, Svyatoslav Ryhel wrote:
> >> Default-tap and default-trim values are used for eMMC setup
> >> mostly on T114+ devices. As for now, those values are hardcoded
> >> for T210 and ignored for all other Tegra generations. Fix this
> >> by passing tap and trim values from dts.
> >> 
> >> This commit will cause regression on T210 (emmc may not work),
> >> fix is applied in tegra210.dtsi and will be sent next week.
> >
> >Heh... I don't think so. If you already know that this will cause a
> >regression on Tegra210 you need to rework this. Adding regressions
> >accidentally is already bad enough, but doing so knowingly is a big
> >no-no.
> 
> DTS change for t210 was sent in "General tegra and board improvements"
> patchset. This is why this pathset contains only 1 (one) patch and a
> warning. It has a dependency.

For U-Boot this may not matter as much because the control DTB is always
linked into the binary, but for Linux for example we need to make sure
that the kernel always remains backwards compatible with older device
trees. I think that's good to follow in general, so making sure there
are sensible defaults to fall back to if the DTB is missing some
properties is good practice.

Anyway, the way you posted these there was a future dependency, so if
someone had applied the driver change without the DTB change having been
applied first this would've caused a regression, which is always bad if
it happens at random points because it makes things like bisections very
painful.

So unless the patch is fixed to fall back to defaults for Tegra210 we
need to carefully coordinate in which order these patches go in. The DT
change needs to go in first, followed by the driver change that relies
on the DTB update.

Thierry

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]