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From: Jassi Brar <jassisinghbrar@gmail.com>
To: viresh kumar <viresh.kumar@st.com>
Cc: Pratyush ANAND <pratyush.anand@st.com>,
	Rajeev KUMAR <rajeev-dlh.kumar@st.com>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>,
	Bhupesh SHARMA <bhupesh.sharma@st.com>,
	Shiraz HASHIM <shiraz.hashim@st.com>,
	"Koul, Vinod" <vinod.koul@intel.com>,
	"linus.walleij@linaro.org" <linus.walleij@linaro.org>,
	Vipin KUMAR <vipin.kumar@st.com>,
	"spi-devel-general@lists.sourceforge.net"
	<spi-devel-general@lists.sourceforge.net>,
	"grant.likely@secretlab.ca" <grant.likely@secretlab.ca>,
	Armando VISCONTI <armando.visconti@st.com>,
	Amit VIRDI <Amit.VIRDI@st.com>,
	Vipul Kumar SAMAR <vipulkumar.samar@st.com>,
	"viresh.linux@gmail.com" <viresh.linux@gmail.com>,
	Deepak SIKRI <deepak.sikri@st.com>,
	Bhavna YADAV <bhavna.yadav@st.com>,
	Dan Williams <dan.j.williams@intel.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH V2 6/6] spi/spi-pl022: Request/free DMA channels as and when required.
Date: Wed, 10 Aug 2011 15:39:28 +0530	[thread overview]
Message-ID: <CABb+yY0Qvuhrn+FUhWDHMwUjv=nR4MOfLeDfTzG17HXEuu2pmA@mail.gmail.com> (raw)
In-Reply-To: <4E424F7B.2000800@st.com>

On Wed, Aug 10, 2011 at 2:59 PM, viresh kumar <viresh.kumar@st.com> wrote:
> On 08/10/2011 02:30 PM, Russell King - ARM Linux wrote:
>>> > They must be allocated when they are required and must be freed after we are
>>> > done with transfers. So that they can be used by other users.
>> Which DMA engine driver requires this?
>>
>
> dw_dmac.c
>
>> Normally, when we have DMA engine drivers with multiple request signals,
>> the slave peripheral side publishes several virtual channels which are
>> claimed by the peripheral drivers.  This (amongst other things) allows
>> the peripheral drivers to hold claim to one of the virtual channels
>> all the time that it's required.
>
> If users of DMA expect DMA engine drivers to work this way, then we should
> have this mentioned clearly in DMA slave documentation.

The requirement stems from the fact that most DMACs(esp third party) could be
made to reroute req-signals by the platform, it has not much to do with the API.
IMO, all dmac drivers should be implemented that way to be on the safer side.

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  parent reply	other threads:[~2011-08-10 10:09 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-08-10  8:50 [PATCH V2 0/6] spi/spi-pl022 fixes Viresh Kumar
2011-08-10  8:50 ` [PATCH V2 1/6] spi/spi-pl022: Resolve formatting issues Viresh Kumar
2011-09-20 17:17   ` Grant Likely
     [not found] ` <cover.1312965741.git.viresh.kumar-qxv4g6HH51o@public.gmane.org>
2011-08-10  8:50   ` [PATCH V2 2/6] spi/spi-pl022: Use GFP_ATOMIC for allocation from tasklet Viresh Kumar
2011-08-10  8:50   ` [PATCH V2 3/6] spi/spi-pl022: Don't allocate more sg than required Viresh Kumar
2011-08-10  8:54     ` Russell King - ARM Linux
2011-08-10  9:05       ` viresh kumar
2011-08-10 11:42     ` Sergei Shtylyov
2011-08-10 11:46       ` viresh kumar
2011-08-10  8:50   ` [PATCH V2 4/6] spi/spi-pl022: calculate_effective_freq() must set rate <= requested rate Viresh Kumar
2011-08-10  8:50   ` [PATCH V2 5/6] spi/spi-pl022: Call pl022_dma_remove(pl022) only if enable_dma is true Viresh Kumar
2011-08-10  8:50 ` [PATCH V2 6/6] spi/spi-pl022: Request/free DMA channels as and when required Viresh Kumar
2011-08-10  9:00   ` Russell King - ARM Linux
2011-08-10  9:29     ` viresh kumar
2011-08-10 10:01       ` Koul, Vinod
     [not found]         ` <438BB0150E931F4B9CE701519A4463010871804A15-qq4HA3s+46oFyVwBAnZdSLfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2011-08-10 10:14           ` viresh kumar
2011-08-10 10:32             ` Russell King - ARM Linux
2011-08-10 16:53               ` Koul, Vinod
2011-08-10 10:29         ` Russell King - ARM Linux
2011-08-10 10:31         ` Jassi Brar
2011-08-10 10:40           ` Russell King - ARM Linux
2011-08-10 11:24             ` Jassi Brar
2011-08-10 11:54               ` Linus Walleij
2011-08-10 13:16                 ` Jassi Brar
2011-08-10 20:58                   ` Vinod Koul
2011-08-10 18:59                     ` Jassi Brar
2011-08-16 11:55                       ` Koul, Vinod
2011-08-16 14:51                         ` Jassi Brar
2011-08-19 13:49                           ` Koul, Vinod
2011-08-11 12:55                   ` Linus Walleij
2011-08-11 14:22                     ` Jassi Brar
2011-08-11 14:48                       ` Linus Walleij
     [not found]                         ` <CAKnu2MptC8HWCNo6W+X9rawn6MCwAe3DB3B5UcHD1tCD9tA2cg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-08-11 17:05                           ` Jassi Brar
2011-08-11 22:35                         ` Koul, Vinod
2011-08-10 10:09       ` Jassi Brar [this message]
     [not found]         ` <CABb+yY0Qvuhrn+FUhWDHMwUjv=nR4MOfLeDfTzG17HXEuu2pmA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-08-10 10:30           ` Russell King - ARM Linux
2011-08-10 10:48             ` Jassi Brar
2011-08-10 11:42 ` [PATCH V3 3/6] spi/spi-pl022: Don't allocate more sg than required Viresh Kumar
2011-09-01 10:04 ` [PATCH V2 0/6] spi/spi-pl022 fixes Viresh Kumar
2011-09-01 10:56   ` Linus Walleij
     [not found]     ` <CACRpkdYeq9in+U_tyvb=yVuX2t5TnkUSsO+BozUGVJwZVh+4Ag-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-09-20 11:16       ` Viresh Kumar
2011-09-20 17:23         ` Grant Likely

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