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From: Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
To: Eli Billauer <eli.billauer-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: devel-gWbeCf7V1WCQmaza687I9mD2FQJk+8+b@public.gmane.org,
	Shuah Khan <shuah.kh-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	discuss-Wa75r+71Mmgdnm+yROfE0A@public.gmane.org,
	gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	bhelgaas-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
	linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH v2 1/4] dma-mapping: Add devm_ interface for dma_map_single()
Date: Wed, 4 Jun 2014 23:25:25 +0200	[thread overview]
Message-ID: <20140604212525.GE23880@8bytes.org> (raw)
In-Reply-To: <538F3548.4050101-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

Hi,

On Wed, Jun 04, 2014 at 06:03:36PM +0300, Eli Billauer wrote:
> I believe that I need a managed dma_map_single() my own driver,
> which doesn't fall in the case of a single use: The driver allocates
> its buffers with __get_free_pages() (or the to-be managed version of
> it). Then it cuts the allocated memory into smaller buffers (in some
> cases, and with certain alignment rules), and  then calls
> dma_map_single() to do the DMA mapping for each. The buffers are
> held along the driver's lifetime, with DMA sync API juggling control
> back and forth to the hardware. Note that the DMA is noncoherent.

What you are trying to do should work with dma_alloc_noncoherent(). The
API allows partial syncs on this memory, so you should be fine.

The problem with a devm variant of dma_map_* is that it is too easy to
misuse or to use it wrong so that a driver could eat up all available
DMA handles on some platforms.


	Joerg

WARNING: multiple messages have this Message-ID (diff)
From: Joerg Roedel <joro@8bytes.org>
To: Eli Billauer <eli.billauer@gmail.com>
Cc: Tejun Heo <tj@kernel.org>, Shuah Khan <shuah.kh@samsung.com>,
	devel@driverdev.osuosl.org, gregkh@linuxfoundation.org,
	bhelgaas@google.com, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, iommu@lists.linux-foundation.org,
	discuss@x86-64.org
Subject: Re: [PATCH v2 1/4] dma-mapping: Add devm_ interface for dma_map_single()
Date: Wed, 4 Jun 2014 23:25:25 +0200	[thread overview]
Message-ID: <20140604212525.GE23880@8bytes.org> (raw)
In-Reply-To: <538F3548.4050101@gmail.com>

Hi,

On Wed, Jun 04, 2014 at 06:03:36PM +0300, Eli Billauer wrote:
> I believe that I need a managed dma_map_single() my own driver,
> which doesn't fall in the case of a single use: The driver allocates
> its buffers with __get_free_pages() (or the to-be managed version of
> it). Then it cuts the allocated memory into smaller buffers (in some
> cases, and with certain alignment rules), and  then calls
> dma_map_single() to do the DMA mapping for each. The buffers are
> held along the driver's lifetime, with DMA sync API juggling control
> back and forth to the hardware. Note that the DMA is noncoherent.

What you are trying to do should work with dma_alloc_noncoherent(). The
API allows partial syncs on this memory, so you should be fine.

The problem with a devm variant of dma_map_* is that it is too easy to
misuse or to use it wrong so that a driver could eat up all available
DMA handles on some platforms.


	Joerg



  parent reply	other threads:[~2014-06-04 21:25 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-01  7:01 [PATCH v2 0/4] devres: dma-mapping: Introducing new functions Eli Billauer
2014-06-01  7:01 ` [PATCH v2 1/4] dma-mapping: Add devm_ interface for dma_map_single() Eli Billauer
2014-06-01  7:01   ` Eli Billauer
2014-06-03 21:24   ` Shuah Khan
     [not found]     ` <538E3D04.9060808-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
2014-06-03 23:39       ` Joerg Roedel
2014-06-03 23:39         ` Joerg Roedel
2014-06-04 14:04         ` Tejun Heo
2014-06-04 14:04           ` Tejun Heo
     [not found]           ` <20140604140408.GC5004-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org>
2014-06-04 14:12             ` Joerg Roedel
2014-06-04 14:12               ` Joerg Roedel
2014-06-04 14:14               ` Tejun Heo
2014-06-04 14:14                 ` Tejun Heo
2014-06-04 15:03                 ` Eli Billauer
2014-06-04 15:03                   ` Eli Billauer
     [not found]                   ` <538F3548.4050101-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2014-06-04 21:25                     ` Joerg Roedel [this message]
2014-06-04 21:25                       ` Joerg Roedel
     [not found]                       ` <20140604212525.GE23880-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
2014-06-06 11:45                         ` Eli Billauer
2014-06-06 11:45                           ` Eli Billauer
     [not found]                           ` <5391A9C2.3040602-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2014-06-06 16:01                             ` Greg KH
2014-06-06 16:01                               ` Greg KH
     [not found]                               ` <20140606160103.GG15110-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2014-06-06 16:21                                 ` Eli Billauer
2014-06-06 16:21                                   ` Eli Billauer
2014-06-06 17:02                                   ` Shuah Khan
2014-06-07 11:23                                     ` Eli Billauer
2014-06-07 11:23                                       ` Eli Billauer
2014-06-01  7:01 ` [PATCH v2 2/4] dma-mapping: Add devm_ interface for dma_map_single_attrs() Eli Billauer
2014-06-01  7:01   ` Eli Billauer
2014-06-01  7:01 ` [PATCH v2 3/4] dma-mapping: pci: Add devm_ interface for pci_map_single Eli Billauer
2014-06-01  7:01 ` [PATCH v2 4/4] staging: xillybus: Use devm_ API for memory allocation and DMA mapping Eli Billauer

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