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From: 'Christoph Hellwig' <hch@lst.de>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	'Christoph Hellwig' <hch@lst.de>,
	Dominik Brodowski <linux@dominikbrodowski.net>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR
Date: Fri, 25 Sep 2020 06:14:25 +0200	[thread overview]
Message-ID: <20200925041425.GA9419@lst.de> (raw)
In-Reply-To: <f9c37e5ff1cb4a02bff6d2a8d0ea2dcc@AcuMS.aculab.com>

On Tue, Sep 22, 2020 at 01:56:46PM +0000, David Laight wrote:
> > +/*
> > + * 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.

This is what I've committed:

 * 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.  It is specific to a
 * given device and there may be a translation between the CPU physical address
 * space and the bus address space.
_______________________________________________
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iommu@lists.linux-foundation.org
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WARNING: multiple messages have this Message-ID (diff)
From: 'Christoph Hellwig' <hch@lst.de>
To: David Laight <David.Laight@ACULAB.COM>
Cc: 'Christoph Hellwig' <hch@lst.de>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Dominik Brodowski <linux@dominikbrodowski.net>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR
Date: Fri, 25 Sep 2020 06:14:25 +0200	[thread overview]
Message-ID: <20200925041425.GA9419@lst.de> (raw)
In-Reply-To: <f9c37e5ff1cb4a02bff6d2a8d0ea2dcc@AcuMS.aculab.com>

On Tue, Sep 22, 2020 at 01:56:46PM +0000, David Laight wrote:
> > +/*
> > + * 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.

This is what I've committed:

 * 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.  It is specific to a
 * given device and there may be a translation between the CPU physical address
 * space and the bus address space.

  reply	other threads:[~2020-09-25  4:14 UTC|newest]

Thread overview: 14+ 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 13:39 ` Christoph Hellwig
2020-09-22 13:40 ` [PATCH 1/3] dma-mapping: remove DMA_MASK_NONE Christoph Hellwig
2020-09-22 13:40   ` Christoph Hellwig
2020-09-22 13:59   ` Dominik Brodowski
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   ` 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 13:40   ` Christoph Hellwig
2020-09-22 13:56   ` David Laight
2020-09-22 13:56     ` David Laight
2020-09-25  4:14     ` 'Christoph Hellwig' [this message]
2020-09-25  4:14       ` 'Christoph Hellwig'

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