linux-kernel - Re: [PATCH v4 2/2] dma: replace zone_dma_bits by zone_dma

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Message-ID: <Zqtew0ra4opFgl9l@arm.com>
Date: Thu, 1 Aug 2024 11:09:07 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Baruch Siach <baruch@...s.co.il>
Cc: Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org,
	Petr Tesařík <petr@...arici.cz>,
	Ramon Fried <ramon@...reality.ai>,
	Elad Nachman <enachman@...vell.com>
Subject: Re: [PATCH v4 2/2] dma: replace zone_dma_bits by zone_dma_limit

On Thu, Aug 01, 2024 at 11:25:07AM +0300, Baruch Siach wrote:
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 9b5ab6818f7f..c45e2152ca9e 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -115,35 +115,35 @@ static void __init arch_reserve_crashkernel(void)
>  }
>  
>  /*
> - * Return the maximum physical address for a zone accessible by the given bits
> - * limit. If DRAM starts above 32-bit, expand the zone to the maximum
> + * Return the maximum physical address for a zone given its limit.
> + * If DRAM starts above 32-bit, expand the zone to the maximum
>   * available memory, otherwise cap it at 32-bit.
>   */
> -static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
> +static phys_addr_t __init max_zone_phys(phys_addr_t zone_limit)
>  {
> -	phys_addr_t zone_mask = DMA_BIT_MASK(zone_bits);
>  	phys_addr_t phys_start = memblock_start_of_DRAM();
>  
>  	if (phys_start > U32_MAX)
> -		zone_mask = PHYS_ADDR_MAX;
> -	else if (phys_start > zone_mask)
> -		zone_mask = U32_MAX;
> +		zone_limit = PHYS_ADDR_MAX;
> +	else if (phys_start > zone_limit)
> +		zone_limit = U32_MAX;
>  
> -	return min(zone_mask, memblock_end_of_DRAM() - 1) + 1;
> +	return min(zone_limit, memblock_end_of_DRAM() - 1) + 1;
>  }

OK, so no functional change here which is good. But isn't this series
missing some additional patches to limit ZONE_DMA? For you platform, the
above function expands ZONE_DMA to the whole RAM which IIUC it's not
what you want eventually.

-- 
Catalin