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Date:   Mon, 7 Jun 2021 15:38:57 +0530
From:   Vinod Koul <vkoul@kernel.org>
To:     Olivier Dautricourt <olivier.dautricourt@orolia.com>
Cc:     Rob Herring <robh+dt@kernel.org>, Stefan Roese <sr@denx.de>,
        dmaengine@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 3/3] dmaengine: altera-msgdma: add OF support
Message-ID: <YL3wOT1B8Qp+EXSV@vkoul-mobl>
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 <YL3DvQWhn+SsBqhJ@vkoul-mobl>
 <YL3Ynm9xBQ419qK3@orolia.com>
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On 07-06-21, 10:28, Olivier Dautricourt wrote:
> 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@denx.de>
> > > Signed-off-by: Olivier Dautricourt <olivier.dautricourt@orolia.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.

Yeah no point in adding filter_fn. I guess we need
of_dma_xlate_by_chan_id() here, I guess you are specifying channel in dts
right? If not above would be okay

> >
> > > +
> > >  /**
> > >   * 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.

Well including in CONFIG_OF sounded protection from compilation which is
not required.

Now the issue is that you maybe running on a system which may or maynot
have DT and even on DT based systems your device may not be DT one..

So i think the return should be handled here if DT device is not present
and warn that and continue for not DT modes.. Also someone who has this
non DT device should test the changes


Thanks
-- 
~Vinod