From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Viresh Kumar <viresh.kumar@st.com>
Cc: pratyush.anand@st.com, rajeev-dlh.kumar@st.com,
bhavna.yadav@st.com, bhupesh.sharma@st.com,
armando.visconti@st.com, linus.walleij@linaro.org,
jassisinghbrar@gmail.com, vipin.kumar@st.com,
grant.likely@secretlab.ca, shiraz.hashim@st.com,
amit.virdi@st.com, vipulkumar.samar@st.com,
viresh.linux@gmail.com, deepak.sikri@st.com,
spi-devel-general@lists.sourceforge.net,
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 10:00:42 +0100 [thread overview]
Message-ID: <20110810090042.GE1831@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <566c0525199f498f04422d4c3b2ddd7466648c20.1312965742.git.viresh.kumar@st.com>
On Wed, Aug 10, 2011 at 02:20:59PM +0530, Viresh Kumar wrote:
> Currently we request DMA channels at probe time and free them at remove. They
> are always occupied, irrespective of their usage.
>
> 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?
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.
This actually results in better usage of the DMA controller, as the
virtual channels can be assigned to physical channels dynamically
according to what the physical channels are doing.
Plus, actually, the idea that DMA channels should be a short-term thing
is broken as soon as you start considering things like UARTs, where you
need a channel tied up long-term for the receive side of things.
next prev parent reply other threads:[~2011-08-10 9:00 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 [this message]
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
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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