[U-Boot] [PATCH 3/9] SPL: read and store arch property from U-Boot image

[Andre Przywara]

On Thu, 21 Feb 2019 12:47:04 +0100
Alexander Graf <agraf at suse.de> wrote:

Hi Alex,

> On 02/21/2019 02:30 AM, Andre Przywara wrote:
> > Read the specified "arch" value from a legacy or FIT U-Boot image and
> > store it in our SPL data structure.
> > This allows loaders to take the target architecture in account for
> > custom loading procedures.
> > Having the complete string -> arch mapping for FIT based images in the
> > SPL would be too big, so we leave it up to architectures (or boards) to
> > overwrite the weak function that does the actual translation, possibly
> > covering only the required subset there.
> >
> > Signed-off-by: Andre Przywara <andre.przywara at arm.com>  
> 
> Reviewed-by: Alexander Graf <agraf at suse.de>

Thanks for having a look!

> I don't fully buy the argument that the generic mapping would be too big 
> though. Realistically you should be able to get away with 1 or 2 
> branches per case, no? So that would be maybe 40 instructions?

You are apparently not in the Allwinner SPL mindset ;-)
I get excited when I find a way of saving 100 bytes (see the writel_relaxed
patch), so wasting 160 bytes when we will probably never need to return
IH_ARCH_X86_64 doesn't sound right to me.

And Philipp is right: the canonical way would be to use uimage_arch[] from
common/image.c, which is quite big.

We could have a big #ifdef cascade, something like:
+#ifdef CONFIG_ARM
+	if (!strcmp(arch_str, "arm"))
+		return IH_ARCH_ARM;
+
+	if (!strcmp(arch_str, "arm64"))
+		return IH_ARCH_ARM64;
+#endif
+#ifdef CONFIG_X86
+	if (!strcmp(arch_str, "x86"))
+		return IH_ARCH_I386;
+
+	if (!strcmp(arch_str, "x86_64"))
+		return IH_ARCH_X86_64;
+#endif
....

I am just not sure it's worth to introduce this out of the blue *now*,
without use cases and without proper testing.

Cheers,
Andre.