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

[Carlos Song]

> >
> >
> > > -----Original Message-----
> > > From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
> > > Sent: Tuesday, November 26, 2024 6:24 PM
> > > To: Carlos Song <carlos.song@xxxxxxx>
> > > Cc: Frank Li <frank.li@xxxxxxx>; o.rempel@xxxxxxxxxxxxxx;
> > > kernel@xxxxxxxxxxxxxx; andi.shyti@xxxxxxxxxx; shawnguo@xxxxxxxxxx;
> > > s.hauer@xxxxxxxxxxxxxx; festevam@xxxxxxxxx; imx@xxxxxxxxxxxxxxx;
> > > linux-i2c@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > linux-kernel@xxxxxxxxxxxxxxx
> > > 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!
> 

I will apply it in V3. Thank you for your ack!
> > 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"); }
> 
> regards,
> Marc
> 
> --
> Pengutronix e.K.                 | Marc Kleine-Budde          |
> Embedded Linux                   | https://www.pengutronix.de |
> Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
> Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |