linux-kernel - Re: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves

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Date:   Mon, 20 Jan 2020 10:01:51 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Vinod Koul <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        dmaengine@...r.kernel.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves

Hi Peter,

On Fri, Jan 17, 2020 at 9:08 PM Peter Ujfalusi <peter.ujfalusi@...com> wrote:
> On 1/17/20 5:30 PM, Geert Uytterhoeven wrote:
> > Currently it is not easy to find out which DMA channels are in use, and
> > which slave devices are using which channels.
> >
> > Fix this by creating two symlinks between the DMA channel and the actual
> > slave device when a channel is requested:
> >   1. A "slave" symlink from DMA channel to slave device,
>
> Have you considered similar link name as on the slave device:
> slave:<name>
>
> That way it would be easier to grasp which channel is used for what
> purpose by only looking under /sys/class/dma/ and no need to check the
> slave device.

Would this really provide more information?
The device name is already provided in the target of the symlink:

root@...lsch:~# readlink
/sys/devices/platform/soc/e6720000.dma-controller/dma/dma1chan2/slave
../../../ee140000.sd

> >   2. A "dma:<name>" symlink slave device to DMA channel.
> > When the channel is released, the symlinks are removed again.
> > The latter requires keeping track of the slave device and the channel
> > name in the dma_chan structure.
> >
> > Note that this is limited to channel request functions for requesting an
> > exclusive slave channel that take a device pointer (dma_request_chan()
> > and dma_request_slave_channel*()).
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > ---
> > v2:
> >   - Add DMA_SLAVE_NAME macro,
> >   - Also handle channels from FIXME,
> >   - Add backlinks from slave device to DMA channel,
> >
> > On r8a7791/koelsch, the following new symlinks are created:
> >
> >     /sys/devices/platform/soc/
> >     ├── e6700000.dma-controller/dma/dma0chan0/slave -> ../../../e6e20000.spi
> >     ├── e6700000.dma-controller/dma/dma0chan1/slave -> ../../../e6e20000.spi
> >     ├── e6700000.dma-controller/dma/dma0chan2/slave -> ../../../ee100000.sd
> >     ├── e6700000.dma-controller/dma/dma0chan3/slave -> ../../../ee100000.sd
> >     ├── e6700000.dma-controller/dma/dma0chan4/slave -> ../../../ee160000.sd
> >     ├── e6700000.dma-controller/dma/dma0chan5/slave -> ../../../ee160000.sd
> >     ├── e6700000.dma-controller/dma/dma0chan6/slave -> ../../../e6e68000.serial
> >     ├── e6700000.dma-controller/dma/dma0chan7/slave -> ../../../e6e68000.serial
> >     ├── e6720000.dma-controller/dma/dma1chan0/slave -> ../../../e6b10000.spi
> >     ├── e6720000.dma-controller/dma/dma1chan1/slave -> ../../../e6b10000.spi
> >     ├── e6720000.dma-controller/dma/dma1chan2/slave -> ../../../ee140000.sd
> >     ├── e6720000.dma-controller/dma/dma1chan3/slave -> ../../../ee140000.sd
> >     ├── e6b10000.spi/dma:rx -> ../e6720000.dma-controller/dma/dma1chan1
> >     ├── e6b10000.spi/dma:tx -> ../e6720000.dma-controller/dma/dma1chan0
> >     ├── e6e20000.spi/dma:rx -> ../e6700000.dma-controller/dma/dma0chan1
> >     ├── e6e20000.spi/dma:tx -> ../e6700000.dma-controller/dma/dma0chan0
> >     ├── e6e68000.serial/dma:rx -> ../e6700000.dma-controller/dma/dma0chan7
> >     ├── e6e68000.serial/dma:tx -> ../e6700000.dma-controller/dma/dma0chan6
> >     ├── ee100000.sd/dma:rx -> ../e6700000.dma-controller/dma/dma0chan3
> >     ├── ee100000.sd/dma:tx -> ../e6700000.dma-controller/dma/dma0chan2
> >     ├── ee140000.sd/dma:rx -> ../e6720000.dma-controller/dma/dma1chan3
> >     ├── ee140000.sd/dma:tx -> ../e6720000.dma-controller/dma/dma1chan2
> >     ├── ee160000.sd/dma:rx -> ../e6700000.dma-controller/dma/dma0chan5
> >     └── ee160000.sd/dma:tx -> ../e6700000.dma-controller/dma/dma0chan4


Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds