linux-kernel - Re: [PATCH v2] i2c: imx: support DMA defer probing

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Message-ID:
 <AM0PR0402MB3937944D3D0D985367EDEF9BE8282@AM0PR0402MB3937.eurprd04.prod.outlook.com>
Date: Wed, 27 Nov 2024 07:41:38 +0000
From: Carlos Song <carlos.song@....com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
CC: Frank Li <frank.li@....com>, "o.rempel@...gutronix.de"
	<o.rempel@...gutronix.de>, "kernel@...gutronix.de" <kernel@...gutronix.de>,
	"andi.shyti@...nel.org" <andi.shyti@...nel.org>, "shawnguo@...nel.org"
	<shawnguo@...nel.org>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>, "imx@...ts.linux.dev"
	<imx@...ts.linux.dev>, "linux-i2c@...r.kernel.org"
	<linux-i2c@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] i2c: imx: support DMA defer probing

> >
> >
> > > -----Original Message-----
> > > From: Marc Kleine-Budde <mkl@...gutronix.de>
> > > Sent: Tuesday, November 26, 2024 6:24 PM
> > > To: Carlos Song <carlos.song@....com>
> > > Cc: Frank Li <frank.li@....com>; o.rempel@...gutronix.de;
> > > kernel@...gutronix.de; andi.shyti@...nel.org; shawnguo@...nel.org;
> > > s.hauer@...gutronix.de; festevam@...il.com; imx@...ts.linux.dev;
> > > linux-i2c@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> > > linux-kernel@...r.kernel.org
> > > Subject: [EXT] Re: [PATCH v2] i2c: imx: support DMA defer probing
> > >
> > > On 26.11.2024 10:15:27, Carlos Song wrote:
> > > > > >  static void i2c_imx_dma_callback(void *arg) @@ -1803,6
> > > > > > +1804,13 @@ static int i2c_imx_probe(struct platform_device *pdev)
> > > > > >  	if (ret == -EPROBE_DEFER)
> > > > > >  		goto clk_notifier_unregister;
> > > > > >
> > > > > > +	/* Init DMA config if supported */
> > > > > > +	ret = i2c_imx_dma_request(i2c_imx, phy_addr);
> > > > > > +	if (ret == -EPROBE_DEFER) {
> > > > > > +		dev_err(&pdev->dev, "DMA not ready, go defer probe!\n");
> > > > > > +		goto clk_notifier_unregister;
> > > > > > +	}
> > > > >
> > > > > Don't spam the logs if the driver defers probing, it's not a error.
> > > > > And it looks strange to ignore all other errors here. Either add
> > > > > a comment here, something like "continue without DMA", or let
> > > > > the function return
> > > > > 0 in case the driver should continue and propagate the error if
> > > > > the caller should take care of it.
> > > > >
> > > >
> > > > Hi,
> > > > Thank you for your suggestion! I agree with you.
> > > > I will change to this logic:
> > > > 	ret = i2c_imx_dma_request(i2c_imx, phy_addr);
> > > > 	if (ret) {
> > > > 		if (ret == -EPROBE_DEFER)
> > > > 			goto clk_notifier_unregister;
> > > > 		dev_info(&pdev->dev, "use pio mode\n");
> > > > 	}
> > > >
> > > > Ret = 0  ----->  enable DMA successfully  -------> no print
> > > > Ret!=0  ----->  defer probe ---------> no print and try again
> > > > Ret!=0  ----->  fail to enable DMA ------> remind now is using pio
> > > > mode
> > > >
> > > > Do you think the logic is acceptable?
> > >
> > > Yes, the other option is to move the logic into
> > > i2c_imx_dma_request() and let it return 0 in case of DMA or fallback
> > > to PIO, or an error in case of probe defer or a fatal error.
> > >
> > > This way the probe function will look like this:
> > >
> > >      ret = i2c_imx_dma_request(i2c_imx, phy_addr);
> > >      if (ret)
> > >                 return dev_err_probe(&pdev->dev, ret, "Failed to
> > > setup DMA\n");
> > >
> >
> > Sorry, I have some different ideas...
> > 1. 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.
> 
> ACK
> 
> >   If we use return dev_err_probe(), we have to return error at
> i2c_imx_dma_request() for "some fatal error", it will cause i2c_adapter can not
> be registered, then kill i2c adapter register.
> 
> i2c_imx_dma_request should only return an error if PIO mode is not an option.
> 
> >   If we always return 0 at i2c_imx_dma_request(), dev_err_probe will not
> work forever. So from my point, if DMA is not working well, just output a log to
> remind now i2c is always
> >   working at CPU mode, we have no DMA, this is enough.
> 
> ACK
> 
> > 2. when really defer probe, return dev_err_probe will return defer probe
> directly, but we still need to goto clk_notifier_unregister branch to free irq,
> clk_notifier_unregister and disable runtime pm.
> >   So we still need more judgement at probe function to handle this.
> 
> Not quite "dev_err_probe()" will not defer probe directly, the return in "return
> dev_err_probe();" does. This should work:
> 
>         ret = i2c_imx_dma_request(i2c_imx, phy_addr);
>         if (ret) {
>                 dev_err_probe(&pdev->dev, ret, "Failed to setup
> DMA\n");
>                 goto clk_notifier_unregister;
>         }
> 
> 
> > So I prefer this logic:
> 
> This also works, LGTM!
> 
> > ret = i2c_imx_dma_request(i2c_imx, phy_addr); if (ret) {
> > 	if (ret == -EPROBE_DEFER)
> > 		goto clk_notifier_unregister;
> > 	dev_info(&pdev->dev, "use pio mode\n"); }
> 

I have carefully considered your suggestion. 
If DMA fail, i2c needs to show error log indeed.
So I made V3 patch, is it what we expected?


> Marc
> 
> --
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