[PATCH 1/3] ARM: dts: Add headers with constants for MTD partitions

Florian Vaussard florian.vaussard at epfl.ch
Wed Jun 19 05:19:45 EDT 2013


Hello,

Thank you for the review.

On 06/12/2013 03:05 PM, Grant Likely wrote:
> On Tue, 11 Jun 2013 16:48:56 +0200, Florian Vaussard <florian.vaussard at epfl.ch> wrote:
>> These constants can be used to easily declare MTD partitions inside
>> DTS.
>>
>> The constants MTDPART_OFS_* are purposely not included. Indeed,
>> parse_ofpart_partitions() is expecting u64, but a DT cell is u32.
>> Negative constants, as defined by MTDPART_OFS_*, would be wrongly
>
> The DT binding uses the number of cells defined by #address-cells. It is
> not fixed to a u32 or a u64
>

The message was ill-formatted, sorry. As an address cell is u32, and as
parse_ofpart_partitions() is storing the value inside u64 without checking
for sign extension (as one assumes to have only positive offsets),
passing a negative value would require 2 address cells, making it more 
difficult
for the DT user. But as Stephen Warren noticed, it is probably desirable
to specify sizes >= 4GB, thus I will think about a way to easily handle 
such case.

Anyway, MTDPART_OFS_* would probably face the same objection raised by 
you for
MTDPART_SIZ_FULL.

>> interpreted by parse_ofpart_partitions(). Two cells should be
>> used to correctly encode the negative constants, but this breaks
>> current usage.
>
> The binding doesn't even allow for shortcuts like MTDPART_SIZ_FULL. If a
> partition fills the whole device, then the reg property should include
> the actual size. If the code is allowing '0' to be used to mean
> MTDPART_SIZ_FULL, then that is a bug that needs to be fixed.
>

The root problem is that many System on Module, like the Gumstix Overo, are
shipped with various NAND sizes depending on the version or even the 
manufacturing
period. Supporting such a diversity would painfully duplicates lots of DT
code and clutter the arch/arm/boot/dts/ directory with dozens of slightly-
different versions. I believe that determining the NAND size is better done
at probe time, and this is what is currently done in legacy board files:

static struct mtd_partition overo_nand_partitions[] = {
         {
                 .name           = "xloader",
                 .offset         = 0,                    /* Offset = 
0x00000 */
                 .size           = 4 * NAND_BLOCK_SIZE,
                 .mask_flags     = MTD_WRITEABLE
         },

<snip...>

         {
                 .name           = "rootfs",
                 .offset         = MTDPART_OFS_APPEND,   /* Offset = 
0x680000 */
                 .size           = MTDPART_SIZ_FULL,
         },
};

Moreover, I do not see such strict restriction in the OF norm. If I 
refer to IEEE
1275-1994 page 174, for the definition of the "reg" property, it is written:

"The interpretation of the size entries is dependent on the parent bus."

Nevertheless, if such an approach is not acceptable, could we think about an
alternative solution? Like a boolean property "mtd,append-and-fill" that 
would
replace the "reg" property and tell the MTD core to compute the 
partition size
at probe time, like what is currently done with board files?

Best regards,

Florian



More information about the linux-arm-kernel mailing list