[U-Boot] [PATCH 3/4] ARM: renesas: Save boot parameters passed in by ATF

[Eugeniu Rosca]

Hi Tom,

On Tue, Mar 12, 2019 at 03:42:24PM -0400, Tom Rini wrote:
> On Tue, Mar 12, 2019 at 07:59:40PM +0100, Eugeniu Rosca wrote:
> > Hi Marek,
> > 
> > On Tue, Mar 5, 2019 at 4:41 AM Marek Vasut <marek.vasut at gmail.com> wrote:
> > [..]
> > > +.align 8
> > > +.globl rcar_atf_boot_args
> > > +rcar_atf_boot_args:
> > > +       .dword 0
> > > +       .dword 0
> > > +       .dword 0
> > > +       .dword 0
> > > +
> > > +ENTRY(save_boot_params)
> > > +       adr     x8, rcar_atf_boot_args
> > > +       stp     x0, x1, [x8], #16
> > > +       stp     x2, x3, [x8], #16
> > > +       b       save_boot_params_ret
> > > +ENDPROC(save_boot_params)
> > 
> > What about relocating the function to C like in [1] and passing the 4
> > arguments to it from ASM like in [2]?
> > This would allow to:
> >  - reduce asm operations to minimum (mov and bl) and make code transparent.
> >  - avoid custom globals and store the ATF information in some C-defined struct.
> > 
> > [1] https://github.com/ARM-software/arm-trusted-firmware/blob/c48d02bade88b07fa7f43aa44e5217f68e5d047f/bl1/bl1_main.c#L263
> > [2] https://github.com/ARM-software/arm-trusted-firmware/blob/c48d02bade88b07fa7f43aa44e5217f68e5d047f/bl1/aarch32/bl1_exceptions.S#L133
> 
> This is super early in the boot process and I'm really not a fan in
> general of writing and calling C before we have things setup for C calls
> to actually work normally, even more so for small things that can be
> commented to be obvious as to what's going on.

I don't have a strong preference about that. It is just my experience
that Renesas once rewrote the elaborate Bosch-contributed BL2 routine
of enabling the cntfrq_el0 system counter from ASM [1] to C [2]. This
is at the BL1-BL2 boundary, while we are still in EL3, so much earlier
in the boot process. This implementation currently runs on the targets
of our customers.

I am fine with any working solution. Thanks for commenting!

[1] https://github.com/renesas-rcar/arm-trusted-firmware/commit/e23524689abb637b14a2961a305f6cfb43909319
[2] https://github.com/renesas-rcar/arm-trusted-firmware/commit/867d84191319#diff-471251fb86bd634ba14891d950c1440eR177

> -- 
> Tom

Best regards,
Eugeniu.