From: Wolfram Sang <wsa@the-dreams.de>
To: Vinod Koul <vinod.koul@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Magnus Damm <magnus.damm@gmail.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Linux I2C <linux-i2c@vger.kernel.org>,
Linux-sh list <linux-sh@vger.kernel.org>,
Simon Horman <horms@verge.net.au>,
dmaengine@vger.kernel.org
Subject: Re: [PATCH 2/5] i2c: sh_mobile: add DMA support
Date: Thu, 11 Dec 2014 08:37:27 +0100 [thread overview]
Message-ID: <20141211073727.GA1252@katana> (raw)
In-Reply-To: <20141211050226.GJ16827@intel.com>
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> I think this is a limitation of driver may not be for HW. The right model for
> dma_chan is to be viewed as SW channels and not the ones of HW (yes that is
> how most of the drivers use that, but we can improve upon)
>
> If we rework the driver to view dma_chan as SW channels, then you can accept
> multiple channel requests and accept based on if we are able link the channel to
> that peripheral or not.
In my understanding, the DMA driver does exactly that. However, it is
not even loaded at the time the I2C driver wants a channel, so the
dmaengine core defers the probe. That is the problem for optional DMA
channels: we can't know when deferring probe won't help anymore and
don't know when it is time to fall back to PIO.
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WARNING: multiple messages have this Message-ID (diff)
From: Wolfram Sang <wsa@the-dreams.de>
To: Vinod Koul <vinod.koul@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Magnus Damm <magnus.damm@gmail.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Linux I2C <linux-i2c@vger.kernel.org>,
Linux-sh list <linux-sh@vger.kernel.org>,
Simon Horman <horms@verge.net.au>,
dmaengine@vger.kernel.org
Subject: Re: [PATCH 2/5] i2c: sh_mobile: add DMA support
Date: Thu, 11 Dec 2014 07:37:27 +0000 [thread overview]
Message-ID: <20141211073727.GA1252@katana> (raw)
In-Reply-To: <20141211050226.GJ16827@intel.com>
[-- Attachment #1: Type: text/plain, Size: 751 bytes --]
> I think this is a limitation of driver may not be for HW. The right model for
> dma_chan is to be viewed as SW channels and not the ones of HW (yes that is
> how most of the drivers use that, but we can improve upon)
>
> If we rework the driver to view dma_chan as SW channels, then you can accept
> multiple channel requests and accept based on if we are able link the channel to
> that peripheral or not.
In my understanding, the DMA driver does exactly that. However, it is
not even loaded at the time the I2C driver wants a channel, so the
dmaengine core defers the probe. That is the problem for optional DMA
channels: we can't know when deferring probe won't help anymore and
don't know when it is time to fall back to PIO.
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next prev parent reply other threads:[~2014-12-11 7:37 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-07 10:11 [PATCH 0/5] i2c: sh_mobile: add DMA support Wolfram Sang
2014-11-07 10:11 ` Wolfram Sang
2014-11-07 10:11 ` [PATCH 1/5] i2c: sh_mobile: sort includes alphabetically Wolfram Sang
2014-11-07 10:11 ` Wolfram Sang
2014-11-12 16:10 ` Wolfram Sang
2014-11-12 16:10 ` Wolfram Sang
2014-11-07 10:11 ` [PATCH 2/5] i2c: sh_mobile: add DMA support Wolfram Sang
2014-11-07 10:11 ` Wolfram Sang
2014-11-12 16:11 ` Wolfram Sang
2014-11-12 16:11 ` Wolfram Sang
2014-12-09 10:53 ` Geert Uytterhoeven
2014-12-09 10:53 ` Geert Uytterhoeven
2014-12-09 14:09 ` Wolfram Sang
2014-12-09 14:09 ` Wolfram Sang
2014-12-10 5:44 ` Magnus Damm
2014-12-10 5:44 ` Magnus Damm
2014-12-10 8:01 ` Wolfram Sang
2014-12-10 8:01 ` Wolfram Sang
2014-12-10 14:19 ` Laurent Pinchart
2014-12-10 14:19 ` Laurent Pinchart
2014-12-10 14:23 ` Wolfram Sang
2014-12-10 14:23 ` Wolfram Sang
2014-12-11 5:02 ` Vinod Koul
2014-12-11 5:14 ` Vinod Koul
2014-12-11 7:37 ` Wolfram Sang [this message]
2014-12-11 7:37 ` Wolfram Sang
2014-12-11 7:47 ` Laurent Pinchart
2014-12-11 7:47 ` Laurent Pinchart
2014-12-11 8:28 ` Wolfram Sang
2014-12-11 8:28 ` Wolfram Sang
2014-12-11 21:42 ` Laurent Pinchart
2014-12-11 21:42 ` Laurent Pinchart
2014-12-11 21:47 ` Wolfram Sang
2014-12-11 21:47 ` Wolfram Sang
2014-12-11 21:52 ` Laurent Pinchart
2014-12-11 21:52 ` Laurent Pinchart
2014-12-12 11:07 ` Wolfram Sang
2014-12-12 11:07 ` Wolfram Sang
2014-12-15 6:43 ` Vinod Koul
2014-12-15 6:55 ` Vinod Koul
2014-12-15 8:31 ` Geert Uytterhoeven
2014-12-15 8:31 ` Geert Uytterhoeven
2014-12-15 9:06 ` Wolfram Sang
2014-12-15 9:06 ` Wolfram Sang
2014-12-15 9:32 ` Geert Uytterhoeven
2014-12-15 9:32 ` Geert Uytterhoeven
2014-12-15 9:13 ` Vinod Koul
2014-12-15 9:25 ` Vinod Koul
[not found] ` <20141215091314.GQ16827-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2014-12-15 9:42 ` Laurent Pinchart
2014-12-15 9:42 ` Laurent Pinchart
2014-12-15 14:48 ` Vinod Koul
2014-12-15 14:48 ` Vinod Koul
2014-12-15 9:45 ` Wolfram Sang
2014-12-15 9:45 ` Wolfram Sang
2014-12-15 14:50 ` Vinod Koul
2014-12-15 14:50 ` Vinod Koul
2014-11-07 10:11 ` [PATCH 3/5] i2c: sh_mobile: improve success message Wolfram Sang
2014-11-07 10:11 ` Wolfram Sang
2014-11-12 16:12 ` Wolfram Sang
2014-11-12 16:12 ` Wolfram Sang
2014-11-13 0:27 ` Simon Horman
2014-11-13 0:27 ` Simon Horman
2014-11-07 10:11 ` [PATCH 4/5] ARM: shmobile: r8a7790: add DMA nodes for IIC Wolfram Sang
2014-11-07 10:11 ` Wolfram Sang
2014-11-13 0:26 ` Simon Horman
2014-11-13 0:26 ` Simon Horman
2014-11-07 10:11 ` [PATCH 5/5] ARM: shmobile: r8a7791: " Wolfram Sang
2014-11-07 10:11 ` Wolfram Sang
2014-11-13 0:26 ` Simon Horman
2014-11-13 0:26 ` Simon Horman
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