From: Jassi Brar <jassisinghbrar@gmail.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Pratyush ANAND <pratyush.anand@st.com>,
Rajeev KUMAR <rajeev-dlh.kumar@st.com>,
Bhavna YADAV <bhavna.yadav@st.com>,
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>,
"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>,
"spi-devel-general@lists.sourceforge.net"
<spi-devel-general@lists.sourceforge.net>,
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 16:18:42 +0530 [thread overview]
Message-ID: <CABb+yY2T7qEZNLH1E8U+oiLUDQC+fGfrT82KExmOtV09UcqQeQ@mail.gmail.com> (raw)
In-Reply-To: <20110810103052.GI1831@n2100.arm.linux.org.uk>
On Wed, Aug 10, 2011 at 4:00 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Wed, Aug 10, 2011 at 03:39:28PM +0530, Jassi Brar wrote:
>> 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.
>
> No it isn't. It's to do with how the physical channels are used.
IMO, a dmac driver developer sees only two aspects - "virtual channel"
at frontend and
"ReqSig/PhyChan" management at the backend. While ReqSig and Physical Channels
are different h/w entities, the driver developer usually works having
tied them together.
For ex, PL330 has 8 physical channels(ARM calls them threads) and 32
peripheral interfaces(ReqSig),
where as the dmac driver freely allocates 32 virtual channels and
keeps in mind that only 8 peripheral
interfaces can be active at any time.
So I am unable to see how I said something different that you do.
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next prev parent reply other threads:[~2011-08-10 10:48 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
[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 [this message]
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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