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

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Message-ID: <20200828020045.GT3265@brightrain.aerifal.cx>
Date:   Thu, 27 Aug 2020 22:00:48 -0400
From:   Rich Felker <dalias@...c.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] sh: don't allow non-coherent DMA for NOMMU

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@....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