linux-kernel - Re: [PATCH] serial: sh-sci: don't filter on DMA device, use only channel ID

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Message-ID: <Pine.LNX.4.64.1108300931220.19151@axis700.grange>
Date:	Tue, 30 Aug 2011 09:54:04 +0200 (CEST)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Vinod Koul <vinod.koul@...ux.intel.com>
cc:	Magnus Damm <magnus.damm@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	Magnus Damm <damm@...nsource.se>
Subject: Re: [PATCH] serial: sh-sci: don't filter on DMA device, use only
 channel ID

On Mon, 29 Aug 2011, Vinod Koul wrote:

> On Mon, 2011-08-29 at 17:16 +0900, Magnus Damm wrote:
> > On Mon, Aug 29, 2011 at 5:00 PM, Paul Mundt <lethal@...ux-sh.org> wrote:
> > > On Fri, Jun 24, 2011 at 05:17:51PM +0530, Koul, Vinod wrote:
> > >> On Fri, 2011-06-24 at 13:56 +0200, Guennadi Liakhovetski wrote:
> > >> > On some sh-mobile systems there are more than one DMA controllers, that
> > >> > can be used for serial ports. Specifying a DMA device in sh-sci platform
> > >> > data unnecessarily restricts the driver to only use one DMA controller.
> > >> >
> > >> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@....de>
> > >> > ---
> > >> >  drivers/tty/serial/sh-sci.c |   25 ++++++++-----------------
> > >> >  include/linux/serial_sci.h  |    2 --
> > >> >  2 files changed, 8 insertions(+), 19 deletions(-)
> > >> >
> > >> > diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> > >> > index ebd8629..8711f4e 100644
> > >> > --- a/drivers/tty/serial/sh-sci.c
> > >> > +++ b/drivers/tty/serial/sh-sci.c
> > >> > @@ -1295,12 +1295,8 @@ static bool filter(struct dma_chan *chan, void *slave)
> > >> >     dev_dbg(chan->device->dev, "%s: slave ID %d\n", __func__,
> > >> >             param->slave_id);
> > >> >
> > >> > -   if (param->dma_dev == chan->device->dev) {
> > >> > -           chan->private = param;
> > >> > -           return true;
> > >> > -   } else {
> > >> > -           return false;
> > >> > -   }
> > >> > +   chan->private = param;
> > >> > +   return true;
> > >> You should not assign chan->private.
> > >> Please move this  to dma_slave_control API
> > >
> > > I haven't seen any reply to this comment and this patch seems to still be
> > > outstanding, is there an updated version of this patch that I've missed?
> I don't recall seeing any updated version fixing this 

As a matter of fact, when you say "use dma_slave_control API," you 
actually mean the dma_slave_config, right? Then, how is one supposed to 
use it in this case? Shall we be issuing a DMA_SLAVE_CONFIG call inside of 
the filter and check the return code? The problem is, that not all DMA 
controllers on sh-mobile SoCs can service the same slave devices. So, if 
we don't check in the filter we might well get an unsuitable DMA channel.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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