linux-kernel - Re: [PATCH 2/2] xilinx

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Date:   Thu, 15 Dec 2016 15:56:34 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>
Cc:     dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        vinod.koul@...el.com, robh+dt@...nel.org, mark.rutland@....com,
        michal.simek@...inx.com, soren.brinkmann@...inx.com,
        appana.durga.rao@...inx.com, anuragku@...inx.com,
        dan.j.williams@...el.com, CARLOS.PALMINHA@...opsys.com,
        Philipp Zabel <p.zabel@...gutronix.de>
Subject: Re: [PATCH 2/2] xilinx_dma: Add reset support

Hi Ramiro,

(CC'ing Philipp Zabel)

On Thursday 15 Dec 2016 11:26:54 Ramiro Oliveira wrote:
> On 12/14/2016 8:16 PM, Laurent Pinchart wrote:
> > Hi Ramiro,
> > 
> > Thank you for the patch.
> > 
> > On Wednesday 14 Dec 2016 17:18:24 Ramiro Oliveira wrote:
> >> Add a DT property to control an optional external reset line
> >> 
> >> Signed-off-by: Ramiro Oliveira <roliveir@...opsys.com>
> >> ---
> >> 
> >>  drivers/dma/xilinx/xilinx_dma.c | 23 +++++++++++++++++++++++
> >>  1 file changed, 23 insertions(+)
> >> 
> >> diff --git a/drivers/dma/xilinx/xilinx_dma.c
> >> b/drivers/dma/xilinx/xilinx_dma.c index 5c9f11b..b845224 100644
> >> --- a/drivers/dma/xilinx/xilinx_dma.c
> >> +++ b/drivers/dma/xilinx/xilinx_dma.c
> >> @@ -46,6 +46,7 @@
> >>  #include <linux/slab.h>
> >>  #include <linux/clk.h>
> >>  #include <linux/io-64-nonatomic-lo-hi.h>
> >> +#include <linux/reset.h>
> > 
> > I had neatly sorted the header alphabetically until someone added clk.h
> > and io-64-nonatomic-lo-hi.h :-( Could you please move reset.h just before
> > slab.h ?
>
> Sure. Actually I was tempted to reorder it, but I decided not to do it. I'll
> do it now

Yeah, I'll sleep better tonight :-D

> >>  #include "../dmaengine.h"
> >> 
> >> @@ -409,6 +410,7 @@ struct xilinx_dma_device {
> >>  	struct clk *rxs_clk;
> >>  	u32 nr_channels;
> >>  	u32 chan_id;
> >> +	struct reset_control *rst;
> >>  };
> >>  
> >>  /* Macros */
> >> @@ -2543,6 +2545,27 @@ static int xilinx_dma_probe(struct platform_device
> >> *pdev) if (IS_ERR(xdev->regs))
> >>  		return PTR_ERR(xdev->regs);
> >> 
> >> +	xdev->rst = devm_reset_control_get_optional(&pdev->dev, "reset");
> > 
> > devm_reset_control_get_optional() is deprecated as explained in
> > linux/reset.h, you should use devm_reset_control_get_optional_exclusive()
> > or devm_reset_control_get_optional_shared() instead, as applicable.
> > 
> > This being said, I'm wondering why the optional versions of those
> > functions exist, as they do exactly the same as the non-optional versions.
> > The API feels wrong, it should have been modelled like the GPIO API. Feel
> > free to fix it if you want :-) But that's out of scope for this patch.
> 
> I missed the comment stating that devm_reset_control_get_optional() was
> deprecated.
> 
> I could fix it. Your sugestion is modelling these functions like the GPIO
> API?

I think it would be better for driver if the _get_optional functions would 
return an ERR_PTR() for errors and NULL when reset control is not available, 
and then have the rest of the reset controller API accept NULL as a no-op. 
Your implementation would then be

	xdev->rst = devm_reset_control_get_optional_exclusive(&pdev->dev,
							      "reset");
	if (IS_ERR(xdev->rst)) {
		err = PTR_ERR(xdev->rst);
		if (err != -EPROBE_DEFER)
			dev_err(xdev->dev, "error getting reset %d\n", err);
		return err;
	}

	err = reset_control_deassert(xdev->rst);
	if (err) {
		dev_err(xdev->dev, "failed to deassert reset: %d\n", err);
		return err;
	}

That requires modifying the reset controller API, so it's a bit out-of-scope, 
but if you could give it a go, it would be great.

-- 
Regards,

Laurent Pinchart