linux-kernel - Re: [PATCH v5 3/3] dmaengine: altera-msgdma: add OF support

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Date:   Mon, 7 Jun 2021 10:28:14 +0200
From:   Olivier Dautricourt <olivier.dautricourt@...lia.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Stefan Roese <sr@...x.de>,
        dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] dmaengine: altera-msgdma: add OF support

The 06/07/2021 12:29, Vinod Koul wrote:
> On 18-05-21, 15:25, Olivier Dautricourt wrote:
> > This driver had no device tree support.
> >
> > - add compatible field "altr,socfpga-msgdma"
> > - define msgdma_of_xlate, with no argument
> > - register dma controller with of_dma_controller_register
> >
> > Reviewed-by: Stefan Roese <sr@...x.de>
> > Signed-off-by: Olivier Dautricourt <olivier.dautricourt@...lia.com>
> > ---
> >
> > Notes:
> >     Changes in v2:
> >         none
> >
> >     Changes from v2 to v3:
> >         Removed CONFIG_OF #ifdef's and use if (IS_ENABLED(CONFIG_OF))
> >         only once.
> >
> >     Changes from v3 to v4
> >         Reintroduce #ifdef CONFIG_OF for msgdma_match
> >         as it produces a unused variable warning
> >
> >     Changes from v4 to v5
> >         - As per Rob's comments on patch 1/2:
> >           change compatible field from altr,msgdma to
> >           altr,socfpga-msgdma.
> >         - change commit title to fit previous commits naming
> >         - As per Vinod's comments:
> >           - use dma_get_slave_channel instead of dma_get_any_slave_channel which
> >             makes more sense.
> >           - remove if (IS_ENABLED(CONFIG_OF)) for of_dma_controller_register
> >             as it is taken care by the core
> >
> >  drivers/dma/altera-msgdma.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/drivers/dma/altera-msgdma.c b/drivers/dma/altera-msgdma.c
> > index 9a841ce5f0c5..acf0990d73ae 100644
> > --- a/drivers/dma/altera-msgdma.c
> > +++ b/drivers/dma/altera-msgdma.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/module.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/slab.h>
> > +#include <linux/of_dma.h>
> >
> >  #include "dmaengine.h"
> >
> > @@ -784,6 +785,14 @@ static int request_and_map(struct platform_device *pdev, const char *name,
> >       return 0;
> >  }
> >
> > +static struct dma_chan *msgdma_of_xlate(struct of_phandle_args *dma_spec,
> > +                                     struct of_dma *ofdma)
> > +{
> > +     struct msgdma_device *d = ofdma->of_dma_data;
> > +
> > +     return dma_get_slave_channel(&d->dmachan);
> > +}
>
> Why not use of_dma_simple_xlate() instead?
I guess i could, but i don't think i need to define a filter function,
also there is only one possible channel.
>
> > +
> >  /**
> >   * msgdma_probe - Driver probe function
> >   * @pdev: Pointer to the platform_device structure
> > @@ -888,6 +897,13 @@ static int msgdma_probe(struct platform_device *pdev)
> >       if (ret)
> >               goto fail;
> >
> > +     ret = of_dma_controller_register(pdev->dev.of_node,
> > +                                      msgdma_of_xlate, mdev);
> > +     if (ret) {
> > +             dev_err(&pdev->dev, "failed to register dma controller");
> > +             goto fail;
>
> Should this be treated as an error.. the probe will be invoked on non of
> systems too..
Ok, i'm a bit confused,
in v4 those lines were enclosed with 'if (IS_ENABLED(CONFIG_OF)) { }'
when you said to me that it was already taken care by the core i though
that of_dma_controller_register will return 0 on non-of systems.
Now i can add back IS_ENABLED(CONFIG_OF) or discard the ret value.

>
> --
> ~Vinod

Thanks,
--
Olivier