Re: [PATCH v3] dmaengine: mxs: fix driver registering

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Vinod Koul <vkoul@kernel.org>
Cc: Dario Binacchi <dario.binacchi@amarulasolutions.com>,
	linux-kernel@vger.kernel.org, linux-amarula@amarulasolutions.com,
	Michael Trimarchi <michael@amarulasolutions.com>,
	stable@vger.kernel.org, Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Shawn Guo <shawnguo@kernel.org>,
	dmaengine@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3] dmaengine: mxs: fix driver registering
Date: Tue, 13 Sep 2022 17:16:12 +0200	[thread overview]
Message-ID: <20220913151612.GI12909@pengutronix.de> (raw)
In-Reply-To: <Yqs3E0ipEpsCT2T2@matsya>

Hi Vinod,

On Thu, Jun 16, 2022 at 06:58:43AM -0700, Vinod Koul wrote:
> On 14-06-22, 12:17, Dario Binacchi wrote:
> > Driver registration fails on SOC imx8mn as its supplier, the clock
> > control module, is not ready. Since platform_driver_probe(), as
> > reported by its description, is incompatible with deferred probing,
> > we have to use platform_driver_register().
> > 
> > Fixes: a580b8c5429a ("dmaengine: mxs-dma: add dma support for i.MX23/28")
> > Co-developed-by: Michael Trimarchi <michael@amarulasolutions.com>
> > Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
> > Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> > Cc: stable@vger.kernel.org
> > 
> > ---
> > 
> > Changes in v3:
> > - Restore __init in front of mxs_dma_init() definition.
> > 
> > Changes in v2:
> > - Add the tag "Cc: stable@vger.kernel.org" in the sign-off area.
> > 
> >  drivers/dma/mxs-dma.c | 9 +++------
> >  1 file changed, 3 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/dma/mxs-dma.c b/drivers/dma/mxs-dma.c
> > index 994fc4d2aca4..6e90540fedc4 100644
> > --- a/drivers/dma/mxs-dma.c
> > +++ b/drivers/dma/mxs-dma.c
> > @@ -741,7 +741,7 @@ static struct dma_chan *mxs_dma_xlate(struct of_phandle_args *dma_spec,
> >  				     ofdma->of_node);
> >  }
> >  
> > -static int __init mxs_dma_probe(struct platform_device *pdev)
> > +static int mxs_dma_probe(struct platform_device *pdev)
> 
> why drop __init here, if there is a reason for that please split this
> change and document such reason...

The reason for dropping __init comes with this patch. With
platform_driver_probe() the probe function is called only once, during
init time. The problem with platform_driver_probe() is that the probe
function will never be called again when it initially returns
-EPROBE_DEFER. That's a problem for Dario: The clock is not yet
available, the driver defers probe and will never be probed again
when the clock is finally available.

With platform_driver_register() to which this patch switches to the
probe function can be called at any time, thus __init has to be removed.

For what it's worth:

Acked-by: Sascha Hauer <s.hauer@pengutronix.de>

for this patch.

Sascha

> 
> >  {
> >  	struct device_node *np = pdev->dev.of_node;
> >  	const struct mxs_dma_type *dma_type;
> > @@ -839,10 +839,7 @@ static struct platform_driver mxs_dma_driver = {
> >  		.name	= "mxs-dma",
> >  		.of_match_table = mxs_dma_dt_ids,
> >  	},
> > +	.probe = mxs_dma_probe,
> >  };
> >  
> > -static int __init mxs_dma_module_init(void)
> > -{
> > -	return platform_driver_probe(&mxs_dma_driver, mxs_dma_probe);
> > -}
> > -subsys_initcall(mxs_dma_module_init);
> > +module_platform_driver(mxs_dma_driver);
> > -- 
> > 2.32.0
> 
> -- 
> ~Vinod
> 

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