Re: [PATCH 3/3] ARM: start: Place malloc pool within 32-bit address space

[Andrey Smirnov <andrew.smirnov@gmail.com>]

On Mon, Aug 27, 2018 at 2:06 AM Sascha Hauer <s.hauer@pengutronix.de> wrote:
>
> On Thu, Aug 23, 2018 at 08:05:11PM -0700, Andrey Smirnov wrote:
> > Some 64-bit SoC have IP cores whose DMA capability is limited to
> > 32-bits only. To handles such cases introduced DMA_32_BIT_ONLY as well
> > as add the code to make sure that malloc pool (which will be used for
> > DMA buffers) is accessible using 32-bit address.
> >
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> > ---
> >  arch/arm/cpu/Kconfig |  3 +++
> >  arch/arm/cpu/start.c | 23 +++++++++++++++++++++++
> >  drivers/mci/Kconfig  |  1 +
> >  drivers/net/Kconfig  |  1 +
> >  4 files changed, 28 insertions(+)
> >
> > diff --git a/arch/arm/cpu/Kconfig b/arch/arm/cpu/Kconfig
> > index 2359c56b3..d9f68d9d0 100644
> > --- a/arch/arm/cpu/Kconfig
> > +++ b/arch/arm/cpu/Kconfig
> > @@ -3,6 +3,9 @@ comment "Processor Type"
> >  config PHYS_ADDR_T_64BIT
> >       bool
> >
> > +config DMA_32_BIT_ONLY
> > +     bool
> > +
> >  config CPU_32
> >       bool
> >       select HAS_MODULES
> > diff --git a/arch/arm/cpu/start.c b/arch/arm/cpu/start.c
> > index 898f7ae19..3fc322d52 100644
> > --- a/arch/arm/cpu/start.c
> > +++ b/arch/arm/cpu/start.c
> > @@ -203,6 +203,29 @@ __noreturn void barebox_non_pbl_start(unsigned long membase,
> >               }
> >       }
> >
> > +     if (IS_ENABLED(CONFIG_DMA_32_BIT_ONLY) &&
> > +         /* If membase is past 4GiB there's nothing we can do */
> > +         !WARN_ON(membase > U32_MAX)) {
> > +             /*
> > +              * Using SZ_4G against unsigned long will produce
> > +              * warning when compiling for 32-bit machines, so we
> > +              * defined the constant below so we can compare
> > +              * against U32_MAX instead.
> > +              */
> > +             const unsigned long __malloc_end = malloc_end - 1;
> > +
> > +             if (__malloc_end > U32_MAX) {
> > +                     /*
> > +                      * Some ARMv8 SoCs use IP blocks that are
> > +                      * only do DMA transfers in first 4GiB of
> > +                      * address space. To avoid allocating bad
> > +                      * DMA buffers we move our malloc pool to
> > +                      * reside within that region.
> > +                      */
> > +                     malloc_end = U32_MAX + 1;
> > +             }
> > +     }
>
> I suggest to call barebox_arm_entry() with 32bit memory only instead of
> putting that into common code. This is no proper solution anyway, so I
> think we can equally well push that issue back to the SoCs. I may change
> my mind when more SoCs come up with this issue...
>

OK, fair enough. I'll convert v2 to do that.

>
> > diff --git a/drivers/mci/Kconfig b/drivers/mci/Kconfig
> > index 954f957bc..0687841a7 100644
> > --- a/drivers/mci/Kconfig
> > +++ b/drivers/mci/Kconfig
> > @@ -83,6 +83,7 @@ config MCI_IMX
> >  config MCI_IMX_ESDHC
> >       bool "i.MX esdhc"
> >       depends on ARCH_IMX
> > +     select DMA_32_BIT_ONLY if PHYS_ADDR_T_64BIT
>
> Enforcing the 32bit memory limitation at compile time is not very nice
> since it means it is active even when the driver ends up being unused.
> This is not a practical issue currently but consider a newer SoC with a
> newer SD core without this limitation, but which shall be compiled
> together with i.MX8M support.
>

Yeah, that's true. Luckily we won't need that option if I limit memory
size via barebox_arm_entry() as you suggest.

Thanks,
Andrey Smirnov

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