linux-kernel - Re: [PATCH v5] i2c: imx: support DMA defer probing

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Message-ID: <Z2UBfcq6pE-JMUrb@pengutronix.de>
Date: Fri, 20 Dec 2024 06:32:45 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Carlos Song <carlos.song@....com>
Cc: Andi Shyti <andi.shyti@...nel.org>, Frank Li <frank.li@....com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Clark Wang <xiaoning.wang@....com>,
	Ahmad Fatoum <a.fatoum@...gutronix.de>
Subject: Re: [PATCH v5] i2c: imx: support DMA defer probing

On Fri, Dec 20, 2024 at 02:45:09AM +0000, Carlos Song wrote:
> 
> 
> > -----Original Message-----
> > From: Oleksij Rempel <o.rempel@...gutronix.de>
> > Sent: Thursday, December 19, 2024 8:23 PM
> > To: Andi Shyti <andi.shyti@...nel.org>
> > Cc: Carlos Song <carlos.song@....com>; Frank Li <frank.li@....com>;
> > kernel@...gutronix.de; shawnguo@...nel.org; s.hauer@...gutronix.de;
> > festevam@...il.com; linux-i2c@...r.kernel.org; imx@...ts.linux.dev;
> > linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; Clark Wang
> > <xiaoning.wang@....com>; Ahmad Fatoum <a.fatoum@...gutronix.de>
> > Subject: [EXT] Re: [PATCH v5] i2c: imx: support DMA defer probing
> >
> > Caution: This is an external email. Please take care when clicking links or
> > opening attachments. When in doubt, report the message using the 'Report this
> > email' button
> >
> >
> > On Thu, Dec 19, 2024 at 01:02:29PM +0100, Andi Shyti wrote:
> > > Hi Carlos,
> > >
> > > > +   /*
> > > > +    * Init DMA config if supported, -ENODEV means DMA not enabled at
> > > > +    * this platform, that is not a real error, so just remind "only
> > > > +    * PIO mode is used". If DMA is enabled, but meet error when request
> > > > +    * DMA channel, error should be showed in probe error log. PIO mode
> > > > +    * should be available regardless of DMA.
> > > > +    */
> > > > +   ret = i2c_imx_dma_request(i2c_imx, phy_addr);
> > > > +   if (ret) {
> > > > +           if (ret == -EPROBE_DEFER)
> > > > +                   goto clk_notifier_unregister;
> > > > +           else if (ret == -ENODEV)
> > > > +                   dev_dbg(&pdev->dev, "Only use PIO mode\n");
> > > > +           else
> > > > +                   dev_err_probe(&pdev->dev, ret, "Failed to setup
> > > > + DMA, only use PIO mode\n");
> > >
> > > Just for understanding, should we quit in this last case, as well?
> > >
> > > Before we were ignoring ENODEV and EPROBE_DEFER, but now you are
> > > making it clear that other failures like ENOMEM might happen.
> >
> > Good point, dev_err_probe() would not print an error in case of EPROBE_DEFER,
> > but in this case we should only print error and continue with PIO.
> >
> Hi,
> 
> Thank you all very much! As I comment at previous mail:
> DMA mode should be optional for i2c-imx, because i2c-imx can accept DMA mode not enabled, because it still can work in CPU mode.[1]
> [1]https://lore.kernel.org/imx/AM0PR0402MB39374E34FD6133B5E3D414D7E82F2@AM0PR0402MB3937.eurprd04.prod.outlook.com/
> 
> Also we don't want to annoy current user without DMA[2]
> [2] https://lore.kernel.org/imx/20241127-analytic-azure-hamster-727fd8-mkl@pengutronix.de/
> 
> So we make this logic. Anyway we let the I2C controller registered whether DMA is available or not(except defer probe).
> Ignoring ENODEV and EPROBE_DEFER makes it looks like nothing happened if DMA is defer probed or not enabled(This is an expected).
> However we still need i2c DMA status is known when meet an unexpected error, so we use dev_err_probe() to print error.

Why dev_err_probe() instead of dev_err()?

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