From: David Laight <David.Laight@ACULAB.COM>
To: 'Christoph Hellwig' <hch@lst.de>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Dominik Brodowski <linux@dominikbrodowski.net>
Subject: RE: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR
Date: Tue, 22 Sep 2020 13:56:46 +0000 [thread overview]
Message-ID: <f9c37e5ff1cb4a02bff6d2a8d0ea2dcc@AcuMS.aculab.com> (raw)
In-Reply-To: <20200922134002.1227279-4-hch@lst.de>
From: Christoph Hellwig
> Sent: 22 September 2020 14:40
...
> @@ -131,6 +125,16 @@ struct dma_map_ops {
> unsigned long (*get_merge_boundary)(struct device *dev);
> };
>
> +/*
> + * A dma_addr_t can hold any valid DMA or bus address for the platform. It can
> + * be given to a device to use as a DMA source or target. A CPU cannot
> + * reference a dma_addr_t directly because there may be translation between its
> + * physical address space and the bus address space.
It can't access it 'directly' because it isn't a virtual address....
> + *
> + * DMA_MAPPING_ERROR is the magic error code if a mapping failed. It should not
> + * be used directly in drivers, but checked for using dma_mapping_error()
> + * instead.
> + */
I think it might be worth adding:
A dma_addr_t value may be device dependant and differ from the
'physical address' of the memory.
David
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next prev parent reply other threads:[~2020-09-22 13:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 13:39 a few trivial dma-mapping header cleanups Christoph Hellwig
2020-09-22 13:40 ` [PATCH 1/3] dma-mapping: remove DMA_MASK_NONE Christoph Hellwig
2020-09-22 13:59 ` Dominik Brodowski
2020-09-22 13:40 ` [PATCH 2/3] dma-mapping: move valid_dma_direction to dma-direction.h Christoph Hellwig
2020-09-22 13:40 ` [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR Christoph Hellwig
2020-09-22 13:56 ` David Laight [this message]
2020-09-25 4:14 ` 'Christoph Hellwig'
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