OF compatible MTD platform RAM driver ?

[Rune Torgersen]

linuxppc-dev-bounces+runet=innovsys.com at ozlabs.org wrote:
> Hi everybody,
> 
> as part of a ARCH=ppc to ARCH=powerpc migration process, I'm
> looking for an
> OpenFirmware compatible way to handle a RAM-based MTD device.
> 
> On the platform_device based ppc architecture, the
> drivers/mtd/maps/plat-ram.c
> driver handled "mtd-ram" platform devices. There is no such
> driver for the
> OF-based powerpc architecture.
> 
> As a temporary workaround I hacked the physmap_of driver to
> handle "direct-mapped" OF devices oh type "ram" by adding a
> corresponding entry in the of_flash_match[] array. This seems to work
> fine. 
> 
> What would be the preferred way to handle OF-compatible RAM-based MTD
> devices ? The 3 ways I can think of are
> 
> 1. porting the plat-ram driver to OF (the driver isn't used
> in the kernel tree
> but I suspect it is used by out-of-tree boards)
> 
> 2. creating a new plat-ram-of driver, much like the
> physmap_of driver comes
> from the physmap driver
> 
> 3. extending the physmap_of driver to handle RAM devices (in
> which case
> references to "flash" in the function names should probably
> be replaced
> by "mtd")
> 
> I live option 3 better so far.
> 
> Has anyone already worked on this ? Is there any defined
> device tree mapping
> for MTD RAM devices ?
> 
> Best regards,

We ran ito the same issue. 
We did option 3, as it was efinetly the easiest,
here is the sram entry in our dts:

        sram at 9,0 {
            device_type = "rom";
            compatible = "direct-mapped";
            probe-type = "RAM";
            reg = <9 0 20000>;
            bank-width = <2>;
            device-width = <2>;
            #address-cells = <1>;
            #size-cells = <1>;
            partition at 0 {
                label = "SRAM";
                reg = <0 20000>;
            };

here is the change to physmap_of.c:

diff --git a/drivers/mtd/maps/physmap_of.c
b/drivers/mtd/maps/physmap_of.c
old mode 100644
new mode 100755
index aeed9ea..687ef54
--- a/drivers/mtd/maps/physmap_of.c
+++ b/drivers/mtd/maps/physmap_of.c
@@ -201,6 +201,8 @@ static struct mtd_info * __devinit
obsolete_probe(struct of_device *dev,
 		return do_map_probe("cfi_probe", map);
 	} else if (strcmp(of_probe, "JEDEC") == 0) {
 		return do_map_probe("jedec_probe", map);
+	} else if (strcmp(of_probe, "RAM") == 0) {
+		return do_map_probe("map_ram", map);
 	} else {
 		if (strcmp(of_probe, "ROM") != 0)
 			dev_warn(&dev->dev, "obsolete_probe: don't know
probe "