On Wed, May 9, 2018 at 9:41 AM, Himanshu Jha <himanshujha199640@xxxxxxxxx> wrote: > Hi, > > > > The only way to probe an OF driver is when a match is found > in the device table. For an OF-only driver, yes that is generally true. For drivers that support ACPI or platform_data ptr, then it is not true. But what about manually binding a driver via sysfs? > And hence checking for of_match_device() is redundant > and instead it is better to use of_device_get_match_data() to get the > matched driver specific data in the probe function. This part is always true. of_device_get_match_data() was introduced later, so there's still many cases that open code it with of_match_device(). Patches welcome. :) > > For instance: > https://lkml.org/lkml/2018/4/30/66 > > static int mmio_74xx_gpio_probe(struct platform_device *pdev) > { > - const struct of_device_id *of_id; > struct mmio_74xx_gpio_priv *priv; > struct resource *res; > void __iomem *dat; > int err; > > - of_id = of_match_device(mmio_74xx_gpio_ids, &pdev->dev); > - if (!of_id) > - return -ENODEV; > - > priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL); > if (!priv) > return -ENOMEM; > > + priv->flags = (uintptr_t)of_device_get_match_data(&pdev->dev); > + > res = platform_get_resource(pdev, IORESOURCE_MEM, 0); > dat = devm_ioremap_resource(&pdev->dev, res); > if (IS_ERR(dat)) > return PTR_ERR(dat); > > - priv->flags = (uintptr_t) of_id->data; > - > > -------------------------------------------------------------------------- > > In the above example of_match_device() is useless since the > probe occurs *only* when a match is found and therefore checking again > is redundant. > > But now my question is if this is the case, then when does > of_match_device() return NULL ? When is the error handling required ? > > There are places where it is done as "safe-play" coding as suggested to me > by Jonathan Cameron previosuly https://lkml.org/lkml/2018/3/16/1245 > > I am working on a Coccinelle SmPL rule with the help of Julia Lawall to > replace of_match_device() + error handling with > of_device_get_match_data() simply. > > I am testing the refactoring changes and it is at: > https://github.com/himanshujha199640/linux-next/commit/efb7ed923bd00c86fe0a4e67e2ddb636ff0e0ff4 > > ------------------------------------------------------------------------------- > > Some statistics found by Julia Lawall: > > > f_match_device with check: 257/283 > no of tbl: 39, of tbl only: 148, other tbl only: 4, multi tbl: 66 > has of_match_ptr: 87, no of_match_ptr: 170 > > of_match_device without check: 26/283 > no of tbl: 14, of tbl only: 11, other tbl only: 0, multi tbl: 1 > has of_match_ptr: 6, no of_match_ptr: 20 > > of_device_get_match_data with check: 158/212 > no of tbl: 29, of tbl only: 78, other tbl only: 0, multi tbl: 51 > has of_match_ptr: 53, no of_match_ptr: 105 > > of_device_get_match_data without check: 54/212 > no of tbl: 13, of tbl only: 40, other tbl only: 0, multi tbl: 1 > has of_match_ptr: 8, no of_match_ptr: 46 > > Multi table files without an of_match_device check > drivers/mmc/host/mxs-mmc.c > > Multi table files without an of_device_get_match_data check > drivers/clk/clk-versaclock5.c > > of_match_ptr files without an of_match_device check > drivers/pinctrl/mvebu/pinctrl-orion.c > drivers/tty/serial/mvebu-uart.c > drivers/misc/eeprom/eeprom_93xx46.c > arch/arm/plat-pxa/ssp.c > drivers/soc/mediatek/mtk-scpsys.c > drivers/pinctrl/mvebu/pinctrl-armada-cp110.c > of_match_ptr files without an of_device_get_match_data check The purpose of of_match_ptr() is just to increase compile coverage for !CONFIG_OF. In both of these cases, it is perfectly fine to not call of_match_device or of_device_get_match_data if the match table has no data ptr. That is quite common. > drivers/gpu/drm/nouveau/nouveau_platform.c > drivers/gpio/gpio-pxa.c > drivers/gpio/gpio-rcar.c > drivers/iommu/arm-smmu.c > drivers/usb/gadget/udc/renesas_usb3.c > drivers/i2c/busses/i2c-mt65xx.c > drivers/iommu/ipmmu-vmsa.c > drivers/mtd/nand/raw/mtk_ecc.c > > other table only (no of_device_id matching) > drivers/mfd/wm831x-i2c.c > drivers/macintosh/macio_asic.c > drivers/mfd/max14577.c > drivers/mfd/wm831x-spi.c > > -------------------------------------------------------------------------- > > > -- > Himanshu Jha > Undergraduate Student > Department of Electronics & Communication > Guru Tegh Bahadur Institute of Technology > -- > To unsubscribe from this list: send the line "unsubscribe devicetree" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
