linux-kernel - Re: [PATCH] dmaengine: delete redundant chan_id and chancnt initialization in dma drivers

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Message-ID: <CABb+yY2L=wfRoascoriAcnNMKkV7LbQEHCpp78+rCY=aM46x7A@mail.gmail.com>
Date:	Wed, 21 Sep 2011 13:57:27 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Barry Song <Baohua.Song@....com>
Cc:	dan.j.williams@...el.com, Piotr Ziecik <kosmo@...ihalf.com>,
	Jaswinder Singh <jassi.brar@...sung.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Pelagicore AB <info@...agicore.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-kernel@...r.kernel.org, Yong Wang <yong.y.wang@...el.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] dmaengine: delete redundant chan_id and chancnt
 initialization in dma drivers

On Fri, Sep 16, 2011 at 3:13 PM, Barry Song <Baohua.Song@....com> wrote:
> dma_async_device_register will re-init chan_id and chancnt,
> so whatever chan_id and chancnt are set in drivers, they will
> be re-written by dma_async_device_register.
>
> Cc: Nicolas Ferre <nicolas.ferre@...el.com>
> Cc: Viresh Kumar <viresh.kumar@...com>
> Cc: Vinod Koul <vinod.koul@...el.com>
> Cc: Piotr Ziecik <kosmo@...ihalf.com>
> Cc: Yong Wang <yong.y.wang@...el.com>
> Cc: Jaswinder Singh <jassi.brar@...sung.com>
> Cc: Pelagicore AB <info@...agicore.com>
> Signed-off-by: Barry Song <Baohua.Song@....com>
> ---
>  drivers/dma/at_hdmac.c      |    5 ++---
>  drivers/dma/dw_dmac.c       |    5 ++---
>  drivers/dma/intel_mid_dma.c |    2 --
>  drivers/dma/mpc512x_dma.c   |    1 -
>  drivers/dma/pch_dma.c       |    2 --
>  drivers/dma/pl330.c         |    2 --
>  drivers/dma/timb_dma.c      |    3 +--

Apparently ....

drivers/dma/ppc4xx/adma.c
drivers/dma/ipu/ipu_idmac.c
       still write to chan_id.

drivers/dma/amba-pl08x.c
drivers/dma/fsldma.c
drivers/dma/ioat/dma_v2.c
drivers/dma/ioat/dma.c
drivers/dma/mpc512x_dma.c
drivers/dma/shdma.c
       still write to chancnt

Most of them are simply a matter of removal, but some seem
like really depending upon setting them(?)

Anyways, even after you modify those as well, chan_id and chancnt
are rendered overstaying guests in dmaengine core. Because chan_id
of each channel would be _precisely_ the order in which the
_dmac-driver_ added the channel to the 'channels' list.

So if their values are _always_ gonna be just contiguously incrementing
why need variables for that in the dmaengine api?
Dmac drivers could use local variables for that.

OTOH, why not chan_id be left solely for use by dmac drivers read by the
dmaengine only to create sysfs entries ?
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