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@xxxxxxxxx>
> ---
> 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...
> 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.
Sascha
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