linux-kernel - Re: [PATCH v6] i2c: imx: support DMA defer probing

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Message-ID: <abyji6y7ytn7dhhdudslug6esglutwjausunl2nstvjxkveris@vz3jbu5iyhsb>
Date: Wed, 25 Dec 2024 23:42:36 +0100
From: Andi Shyti <andi.shyti@...nel.org>
To: Carlos Song <carlos.song@....com>
Cc: "o.rempel@...gutronix.de" <o.rempel@...gutronix.de>, 
	"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 v6] i2c: imx: support DMA defer probing

Hi Carlos,

On Wed, Dec 25, 2024 at 10:56:34AM +0000, Carlos Song wrote:
> > > > > @@ -1802,6 +1803,18 @@ static int i2c_imx_probe(struct
> > > > > platform_device
> > > > *pdev)
> > > > >       if (ret == -EPROBE_DEFER)
> > > > >               goto clk_notifier_unregister;
> > > > >
> > > > > +     /* As we can always fall back to PIO, let's ignore the error
> > > > > + setting up
> > > > 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(&pdev->dev, "Failed to setup DMA
> > > > > + (%pe),
> > > > only use PIO mode\n",
> > > > > +                             ERR_PTR(ret));
> > > >
> > > > My question here is not just about the use of dev_err vs
> > > > dev_err_probe, but why don't we exit the probe if we get an error.
> > > >
> > > > We should use PIO only in case of ENODEV, in all the other cases I
> > > > think we should just leave. E.g. why don't we exit if we meet ret ==
> > -ENOMEM?
> > >
> > > Hi, Andi
> > >
> > > Thank you! From my point, I2C is critical bus so it should be available as much
> > as possible.
> > > -ENOMEM or other unknown errors all are from i2c_imx_dma_request(). So
> > error happened in enable DMA mode process.
> > 
> > OK, makes sense, it's the idea of "let things fail on their own, I'll move forward as
> > much as I can"; we need to be aware of the choice. Please add a comment
> > above.
> > 
> > But then it's not an error, but a warning. With errors we bail out, with warnings
> > we tell users that something went wrong.
> > 
> > Sorry for keeping you on this point for so long, but do you mind swapping this
> > dev_err in dev_warn, with a comment explaining the reason we decided not to
> > leave?
> > 
> 
> Hi, Andi
> 
> It doesn't matter! I am very happy to receive so many suggestions to help enhance the patch.
> I will do following things at V7:
> 1. Change dev_err to dev_warn
> 2. Use a more detailed comment to explain why we decided not to leave when meet DMA error.

Thank you! I appreciate your responsiveness!

Andi