On Wed, Nov 23, 2022 at 02:23:36PM +0100, Arnd Bergmann wrote: > On Wed, Nov 23, 2022, at 12:33, Thierry Reding wrote: > > On Tue, Nov 22, 2022 at 10:25:50PM +0100, Arnd Bergmann wrote: > >> On Mon, Nov 21, 2022, at 18:12, Thierry Reding wrote: > >> > firmware: tegra: bpmp: Do not support big-endian > >> > >> I pulled the branch, but I think this patch is inconsistent with > >> our normal approach: Since all ARMv7 and ARMv8 processors can > >> run with both big-endian and little-endian kernels, we normally > >> try to keep drivers portable between both ways, even though we > >> don't expect anyone to actually want a big-endian kernel any > >> more. Changing portable code to nonportable code doesn't seem > >> helpful here. > > > > The only reason I dropped this is because the driver is in itself > > inconsistent. Parts of it use byte-swapping for 32-bit values and other > > parts don't. I was originally going to fix big-endian support but it > > would've required changes to the BPMP ABI header to avoid sparse > > warnings in lots of places, then these ABI changes would've needed to > > trickle up to the canonical source, etc. All of that didn't seem worth > > the effort if we couldn't even test this in any way. So the easiest fix > > was to stop pretending and drop the partial support. > > Right > > >> On the other hand, there are already examples of important > >> drivers that are fundamentally incompatible with big-endian > >> mode, notably drivers/efi/, which is required on a lot of > >> machines. > >> > >> You don't have to revert this patch, but it would be helpful > >> to mark code that is explicitly unportable with a 'depends > >> on !CPU_BIG_ENDIAN' line in Kconfig. If you agree, I can > >> add that. > > > > Yes, feel free to add that. > > Added this commit to the soc/drivers branch now: > > commit 4ddb1bf1a83783cebdb174b0efaf62f63ad64e0b > Author: Arnd Bergmann <arnd@xxxxxxxx> > Date: Wed Nov 23 14:21:16 2022 +0100 > > tegra: mark BPMP driver as little-endian only > > The BPMP firmware driver never worked on big-endian kernels, and > cannot easily be made portable. Add a dependency to make this clear > in case anyone ever wants to try a big-endian kernel on this hardware. > > Link: https://lore.kernel.org/linux-arm-kernel/Y34FCQ3xTmcjqKRT@orome/ > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > > diff --git a/drivers/firmware/tegra/Kconfig b/drivers/firmware/tegra/Kconfig > index 1c8ba1f47c7c..cde1ab8bd9d1 100644 > --- a/drivers/firmware/tegra/Kconfig > +++ b/drivers/firmware/tegra/Kconfig > @@ -14,6 +14,7 @@ config TEGRA_IVC > config TEGRA_BPMP > bool "Tegra BPMP driver" > depends on ARCH_TEGRA && TEGRA_HSP_MBOX && TEGRA_IVC > + depends on !CPU_BIG_ENDIAN > help > BPMP (Boot and Power Management Processor) is designed to off-loading > the PM functions which include clock/DVFS/thermal/power from the CPU. Sounds good, thanks. Thierry
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