2018-06-26 10:38 GMT+02:00 Andrew Lunn <andrew@xxxxxxx>: > On Tue, Jun 26, 2018 at 09:44:19AM +0200, Bartosz Golaszewski wrote: >> 2018-06-25 20:02 GMT+02:00 Andrew Lunn <andrew@xxxxxxx>: >> >> With my patch 1/14 you'll get -EPROBE_DEFER from nvmem_cell_get() if >> >> the nvmem provider is not yet registered. Will that help in your case? >> > >> > I don't think so. My driver instantiates the AT24 device. So if i get >> > -EPROBE_DEFER, i need to cleanup the probe, and return -EPROBDE_DEFER >> > to the code. Which means i need to remove the AT24 device... >> > >> > Andrew >> >> Are you sure this is the correct approach? I understand that you want >> to use something like board files for your machine? Wouldn't it be >> better to register a platform device for at24, register a cell lookup >> and then depend on that cell from your driver? > > Hi Bartosz > > The machine is based around a Kontron Com Express module, with an > intel Ivy Bridge CPU. This is then placed into a custom carrier board, > which has a number of i2c devices. > > I have a platform driver which matches on the DMI system ID for the > Kontron module. > > The Com Express module has a PLD which implements i2c, gpio, > etc. There is an MFD for this, which instantiates the i2c-kempld i2c > bus driver. > > My platform driver finds this i2c-kempld bus driver. If it does not > exist yet, it return -EPROBE_DEFER. If it is found it instantiates an > at24 device on it. I need to look at the content of the EEPROM to > determine the hardware revision, plus do a checksum. From that, i > need to instantiates 1 or 2 additional AT24, up to 4 GPIO expanders, > and i2c to spi converter, add some gpio-leds on the gpio expanders, > create a bit-banging MDIO bus, instantiate an Ethernet switch on the > MDIO bus, maybe add an Ethernet switch to the SPI bus, etc. > > As you can see, i have a chain of events. I cannot move onto the next > part of the chain until i know the probe for the previous part has > finished. e.g. i cannot add gpio-leds until i know the gpio expander > has probed. But the gpio expander provides a call back, similar to the > at24 setup(). The MDIO bus and the SPI bus has a mechanism to register > an info structure, just like you have done for NVMEM cells. So that > works out. > > The weak link in this chain is that first at24 probe, and knowing when > i can access the nvmem cells for the revision and checksum > information. -EPROBE_DEFER does not help me here. I need either some > sort of blocking wait for the cells to become available, or a callback > in a context which allows me to instantiate more devices. > > I also have some steps which cannot be undone. You don't provide a > mechanism to unregister the nvmem info structure. The I2C and MDIO > equivalent also does not provide an unregister for bus info. So once i > register the first info structure, i'm past the point of no return. I > cannot return -EPROBE_DEFER because i cannot unregister the info > structures, so that i can register them again the next time the > platform driver gets probed. > > Andrew > I see. I see it this way: the setup callback comes from the time when we didn't have nvmem and should go away. I will protest loud whenever someone will try to use it again and will work towards removing it as soon as possible. I will give your problem a thought and will try to get back with some proposals - maybe we should, as you suggested, extend nvmem even further to allow to remove nvmem info entries etc. Best regards, Bartosz Golaszewski -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
