On Fri, Dec 20, 2024 at 07:38:47AM +0000, Carlos Song wrote: > > > > -----Original Message----- > > From: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> > > Sent: Friday, December 20, 2024 3:35 PM > > To: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> > > Cc: Carlos Song <carlos.song@xxxxxxx>; Andi Shyti <andi.shyti@xxxxxxxxxx>; > > Frank Li <frank.li@xxxxxxx>; kernel@xxxxxxxxxxxxxx; shawnguo@xxxxxxxxxx; > > s.hauer@xxxxxxxxxxxxxx; festevam@xxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx; > > imx@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > > linux-kernel@xxxxxxxxxxxxxxx; Clark Wang <xiaoning.wang@xxxxxxx> > > 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 08:06:25AM +0100, Ahmad Fatoum wrote: > > > Hello Carlos, > > > > > > On 20.12.24 07:58, Carlos Song wrote: > > > > > > > > > > > >> -----Original Message----- > > > >> From: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> > > > >> Sent: Friday, December 20, 2024 2:13 PM > > > >> To: Carlos Song <carlos.song@xxxxxxx> > > > >> Cc: Andi Shyti <andi.shyti@xxxxxxxxxx>; Frank Li > > > >> <frank.li@xxxxxxx>; kernel@xxxxxxxxxxxxxx; shawnguo@xxxxxxxxxx; > > > >> s.hauer@xxxxxxxxxxxxxx; festevam@xxxxxxxxx; > > > >> linux-i2c@xxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx; > > > >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > > >> Clark Wang <xiaoning.wang@xxxxxxx>; Ahmad Fatoum > > > >> <a.fatoum@xxxxxxxxxxxxxx> > > > >> 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 05:59:38AM +0000, Carlos Song wrote: > > > >>>>> 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? > > > >> > > > >> Yes, dev_err_probe() should be used in combination with return. For > > > >> example: > > > >> return dev_err_probe(...); > > > >> > > > >> It will pass the return value on exit of the function and > > > >> optionally print of the error message if it is not EPROBE_DEFER. > > > >> Practically it replace commonly used coding pattern: > > > >> if (ret == -EPROBE_DEFER) { > > > >> return ret; > > > >> } else if (ret) { > > > >> dev_err(..); > > > >> return ret; > > > >> } > > > >> > > > > Hi, > > > > > > > > Get your good point. I will change my code in V6: > > > > + 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, > > only use PIO mode\n"); > > > > + } > > > > > > > > I think this is what you want to see, right? > > > > > > This loses the information why the error happens (ret). Using > > > dev_err_probe even if no probe deferral is expected in that branch is > > > perfectly fine and the kernel-doc even points it out: > > > > > > Using this helper in your probe function is totally fine even if @err > > > is known to never be -EPROBE_DEFER. > > > > Thank you for the feedback. While I recognize the benefits of > > dev_err_probe() for compact and standardized error handling, using it without > > returning its result raises a red flag. > > > > The function's primary purpose is to combine error logging with returning the > > error code. If the return value is not used, it can create confusion and suggests > > potential oversight or unintended behavior. This misuse might mislead readers > > into thinking that the function always returns at that point, which is not the case > > here. > > > > In this scenario, using dev_err() directly is more explicit and avoids any ambiguity > > about the control flow or error handling intent. It keeps the code clear and > > aligned with its actual behavior. > > > > how about this? > > + 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 (%d), only use PIO mode\n", ret); > + } Please use human readable version of error value. In this case it will be: dev_err(&pdev->dev, "Failed to setup DMA (%pe), only use PIO mode\n", ERR_PTR(ret)); -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |