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Date:   Thu, 27 Aug 2020 14:41:32 +0000
From:   Clint Sbisa <csbisa@amazon.com>
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>
CC:     Benjamin Herrenschmidt <benh@amazon.com>,
        Ali Saidi <alisaidi@amazon.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Guy Tzalik <gtzalik@amazon.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
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On Fri, Aug 21, 2020 at 03:51:54PM +0000, Clint Sbisa wrote:
> Using write-combine is crucial for performance of PCI devices where
> significant amounts of transactions go over PCI BARs.
> 
> arm64 supports write-combine PCI mappings, so the appropriate define
> has been added which will expose write-combine mappings under sysfs
> for prefetchable PCI resources.
> 
> Signed-off-by: Clint Sbisa <csbisa@amazon.com>
> ---
>  arch/arm64/include/asm/pci.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/include/asm/pci.h b/arch/arm64/include/asm/pci.h
> index 70b323cf8300..b33ca260e3c9 100644
> --- a/arch/arm64/include/asm/pci.h
> +++ b/arch/arm64/include/asm/pci.h
> @@ -17,6 +17,7 @@
>  #define pcibios_assign_all_busses() \
>  	(pci_has_flag(PCI_REASSIGN_ALL_BUS))
>  
> +#define arch_can_pci_mmap_wc() 1
>  #define ARCH_GENERIC_PCI_MMAP_RESOURCE	1
>  
>  extern int isa_dma_bridge_buggy;
> -- 
> 2.23.3
> 

Ping. Let me know if any more info is needed.

Clint