Re: [PATCH 09/10] sh: don't allow non-coherent DMA for NOMMU

[Rich Felker <dalias@libc.org>]

On Tue, Jul 14, 2020 at 02:18:55PM +0200, Christoph Hellwig wrote:
> The code handling non-coherent DMA depends on being able to remap code
> as non-cached.  But that can't be done without an MMU, so using this
> option on NOMMU builds is broken.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  arch/sh/Kconfig | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
> index f8027eee08edae..337eb496c45a0a 100644
> --- a/arch/sh/Kconfig
> +++ b/arch/sh/Kconfig
> @@ -61,6 +61,7 @@ config SUPERH
>  	select MAY_HAVE_SPARSE_IRQ
>  	select MODULES_USE_ELF_RELA
>  	select NEED_SG_DMA_LENGTH
> +	select NO_DMA if !MMU && !DMA_COHERENT
>  	select NO_GENERIC_PCI_IOPORT_MAP if PCI
>  	select OLD_SIGACTION
>  	select OLD_SIGSUSPEND
> @@ -135,7 +136,7 @@ config DMA_COHERENT
>  	bool

This change broke SD card support on J2 because MMC_SPI spuriously
depends on HAS_DMA. It looks like it can be fixed just by removing
that dependency from drivers/mmc/host/Kconfig.

Rich