linux-kernel - Re: [PATCH RFC v2 4/5] dma-direct: add base offset to zone_dma

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Date: Tue, 18 Jun 2024 22:40:39 +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>,
	Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	iommu@...ts.linux.dev, devicetree@...r.kernel.org,
	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 RFC v2 4/5] dma-direct: add base offset to zone_dma_bits

On Tue, Apr 09, 2024 at 09:17:57AM +0300, Baruch Siach wrote:
> Current code using zone_dma_bits assume that all addresses range in the
> bits mask are suitable for DMA. For some existing platforms this
> assumption is not correct. DMA range might have non zero lower limit.
[...]
> @@ -59,7 +60,7 @@ static gfp_t dma_direct_optimal_gfp_mask(struct device *dev, u64 *phys_limit)
>  	 * zones.
>  	 */
>  	*phys_limit = dma_to_phys(dev, dma_limit);
> -	if (*phys_limit <= zone_dma_limit)
> +	if (*phys_limit <= zone_dma_base + zone_dma_limit)
>  		return GFP_DMA;
>  	if (*phys_limit <= DMA_BIT_MASK(32))
>  		return GFP_DMA32;

As I said previously, we no longer have zone_dma_bits after the first
patch, so adding this limit no longer make sense. In v1, you wanted a
limit like 32G to be added to the 30-bit zone_dma_bits to give you 33G
upper limit for ZONE_DMA. But since the first patch sets zone_dma_limit
to 33G already, this is no longer needed.

-- 
Catalin