linux-kernel - Re: [PATCH] powerpc: enable a 30-bit ZONE

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Date:   Fri, 14 Jun 2019 22:02:35 +0300
From:   Aaro Koskinen <aaro.koskinen@....fi>
To:     Christoph Hellwig <hch@....de>
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        Larry.Finger@...inger.net, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac

Hi,

On Thu, Jun 13, 2019 at 10:24:46AM +0200, Christoph Hellwig wrote:
> With the strict dma mask checking introduced with the switch to
> the generic DMA direct code common wifi chips on 32-bit powerbooks
> stopped working.  Add a 30-bit ZONE_DMA to the 32-bit pmac builds
> to allow them to reliably allocate dma coherent memory.
> 
> Fixes: 65a21b71f948 ("powerpc/dma: remove dma_nommu_dma_supported")
> Reported-by: Aaro Koskinen <aaro.koskinen@....fi>
> Signed-off-by: Christoph Hellwig <hch@....de>

Tested-by: Aaro Koskinen <aaro.koskinen@....fi>

A.

> ---
>  arch/powerpc/include/asm/page.h         | 7 +++++++
>  arch/powerpc/mm/mem.c                   | 3 ++-
>  arch/powerpc/platforms/powermac/Kconfig | 1 +
>  3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> index b8286a2013b4..0d52f57fca04 100644
> --- a/arch/powerpc/include/asm/page.h
> +++ b/arch/powerpc/include/asm/page.h
> @@ -319,6 +319,13 @@ struct vm_area_struct;
>  #endif /* __ASSEMBLY__ */
>  #include <asm/slice.h>
>  
> +/*
> + * Allow 30-bit DMA for very limited Broadcom wifi chips on many powerbooks.
> + */
> +#ifdef CONFIG_PPC32
> +#define ARCH_ZONE_DMA_BITS 30
> +#else
>  #define ARCH_ZONE_DMA_BITS 31
> +#endif
>  
>  #endif /* _ASM_POWERPC_PAGE_H */
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index cba29131bccc..2540d3b2588c 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -248,7 +248,8 @@ void __init paging_init(void)
>  	       (long int)((top_of_ram - total_ram) >> 20));
>  
>  #ifdef CONFIG_ZONE_DMA
> -	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn, 0x7fffffffUL >> PAGE_SHIFT);
> +	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn,
> +			((1UL << ARCH_ZONE_DMA_BITS) - 1) >> PAGE_SHIFT);
>  #endif
>  	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
>  #ifdef CONFIG_HIGHMEM
> diff --git a/arch/powerpc/platforms/powermac/Kconfig b/arch/powerpc/platforms/powermac/Kconfig
> index f834a19ed772..c02d8c503b29 100644
> --- a/arch/powerpc/platforms/powermac/Kconfig
> +++ b/arch/powerpc/platforms/powermac/Kconfig
> @@ -7,6 +7,7 @@ config PPC_PMAC
>  	select PPC_INDIRECT_PCI if PPC32
>  	select PPC_MPC106 if PPC32
>  	select PPC_NATIVE
> +	select ZONE_DMA if PPC32
>  	default y
>  
>  config PPC_PMAC64
> -- 
> 2.20.1
>