Messages in this thread | | | Date | Wed, 28 Oct 2015 08:58:13 +0100 | From | Boris Brezillon <> | Subject | Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node |
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Hi Brian,
On Tue, 27 Oct 2015 10:54:46 -0700 Brian Norris <computersforpeace@gmail.com> wrote:
> Hi Boris, > > On Tue, Oct 27, 2015 at 08:42:00AM +0100, Boris Brezillon wrote: > > On Mon, 26 Oct 2015 19:31:06 -0700 > > Brian Norris <computersforpeace@gmail.com> wrote: > > > > > It seems more logical to use a device node directly associated with the > > > MTD master device (i.e., mtd->dev.of_node field) rather than requiring > > > auxiliary partition parser information to be passed in by the driver in > > > a separate struct. > > > > > > This patch supports the mtd->dev.of_node field, deprecates the parser > > > data 'of_node' field, and begins using the new convention for nand_base. > > > Other NAND driver conversions may now follow. > > > > > > Additional side benefit to assigning mtd->dev.of_node rather than using > > > parser data: the driver core will automatically create a device -> node > > > symlink for us. > > > > I like the idea, but how about pushing the solution even further and > > killing the ->flash_node field which AFAICT is rendered useless by > > your patch? > > I suppose we could do that. I do think there's something to be said for > layering, though. Historically, we haven't done a very good job of > layering in MTD, so low-level drivers often have to poke around in the > MTD structures, even if they really should only have to know a few > things about their helper subsystem/library, like NAND or SPI NOR. So > with that in mind, I think the ->flash_node serves some purpose -- > drivers can just initialize struct nand_chip/spi_nor and be assured that > the NAND/SPI-NOR subsystems will take care of things. > > Now, I don't think there's much reason to suspect that we'd have a more > complex mapping than 1:1 between struct mtd_info and struct nand_chip or > struct spi_nor, so maybe we don't actually need duplicate storage > (mtd.dev.of_node and {spi_nor,nand_chip}.flash_node), and the layering > is just have these APIs: > > nand_set_flash_node() > spi_nor_set_flash_node() > > which just call mtd_set_of_node()?
I'm fine with that, but as you stated in your next answer this is not that simple for the NAND subsystem since a lot of drivers are doing their own custom initialization.
I'll try to come up with something to address that soon (I'll probably revive the nand_chip nand_controller separation series too) based on other subsystems like SPI or I2C. How about providing several simple functions and progressively migrating all NAND controller drivers to it:
struct nand_controller *nand_controller_alloc(struct device *dev, ...); struct nand_chip *nand_alloc(struct nand_controller *ctrl, ...);
...
> > Speaking of layering: why do we have NAND drivers initializing mtd->priv > for us, yet nand_base just assumes that it points to a struct nand_chip?
I guess it's been like this from the beginning, and nobody bothered moving this boilerplate into a function provided by the NAND subsystem.
> And why isn't struct mtd_info just embedded in struct nand_chip?
I always wondered the same thing.
> Are > there ever cases we want more than one (master) MTD per nand_chip? Or > vice versa?
Nope, I'd say that you always have a 1:1 relationship between a master MTD device and a NAND device.
Best Regards,
Boris
-- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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