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

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Message-ID:
 <AM0PR0402MB3937347200BF1967EB677123E8072@AM0PR0402MB3937.eurprd04.prod.outlook.com>
Date: Fri, 20 Dec 2024 05:59:38 +0000
From: Carlos Song <carlos.song@....com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
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



> -----Original Message-----
> From: Oleksij Rempel <o.rempel@...gutronix.de>
> Sent: Friday, December 20, 2024 1:33 PM
> To: Carlos Song <carlos.song@....com>
> Cc: Andi Shyti <andi.shyti@...nel.org>; 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 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://l/
> >
> ore.kernel.org%2Fimx%2FAM0PR0402MB39374E34FD6133B5E3D414D7E82F2
> %40AM0P
> >
> R0402MB3937.eurprd04.prod.outlook.com%2F&data=05%7C02%7Ccarlos.song
> %40
> >
> nxp.com%7C5bfbfc0a74184fa1620808dd20b7c4db%7C686ea1d3bc2b4c6fa92c
> d99c5
> >
> c301635%7C0%7C0%7C638702695851431182%7CUnknown%7CTWFpbGZsb3d
> 8eyJFbXB0e
> >
> U1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIl
> d
> >
> UIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=F28DC7RUwlqd5OIyh5QMVyqa1%2
> F%2BcX2p%2
> > FsFWftgDaliA%3D&reserved=0
> >
> > Also we don't want to annoy current user without DMA[2] [2]
> > https://lore/
> > .kernel.org%2Fimx%2F20241127-analytic-azure-hamster-727fd8-mkl%40peng
> u
> >
> tronix.de%2F&data=05%7C02%7Ccarlos.song%40nxp.com%7C5bfbfc0a74184fa
> 162
> >
> 0808dd20b7c4db%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638
> 7026958
> >
> 51449521%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiI
> wLjAuM
> >
> DAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%
> 7C&s
> >
> data=y6pkewfVx7Mb0ZrPfRwDdAo69TV1eHOkRMnRq91Ec9Q%3D&reserved=0
> >
> > 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()?
>
Hi,
In patch V2 discussion, Marc suggested just return dev_err_probe(), but I don't accept it so I choose to use dev_err_probe() to print error in V3.[1]
In this case, the two APIs have the same function, do you mean dev_err() is more suitable?

[1]https://lore.kernel.org/imx/AM0PR0402MB39374E34FD6133B5E3D414D7E82F2@AM0PR0402MB3937.eurprd04.prod.outlook.com/#t
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