Hi Christopher, Stefano,
Whole series: Acked-by: Nikita Kiryanov nikita@compulab.co.il
On Tue, Jul 12, 2016 at 11:37:33PM +0200, christopher.spinrath@rwth-aachen.de wrote:
Hi,
this is v2 of the series. To address the review comments of v1, v2 has an addtional patch (2/4) touching include/fdt_support.h (thus, I added Simon to the recipients).
The original cover letter was (for a discussion cf. [2]):
this series aims at enhancing support for the cm-fx6 module. In particular, with respect to the upstream linux kernel.
The first patch improves the default environment. It is non-functional but makes it more convenient to adapt certain settings.
The later two patches add mtd partition support for the on-board spi flash chip. They pick up the discussion about specifying a default partitioning in the device tree from here [1]. In short: adding the default partitioning to the device tree was rejected by the linux/ device tree community during mainlining large parts of the device tree. It was proposed to implement the partition/mtd handling in u-boot. On the other hand, it was argued that the flash chip becomes some kind of "black-box" since there will be no partition labeling (in particular, with old u-boot versions).
IMHO defining the mtd partitioning has the following (dis-)advantages:
Advantages:
It is easier for the user to change the partitioning (e.g. to use the unsued 1MB free space).
The flash ship is used entirely for u-boot. So it is quite natural that u-boot manages it. Also, moving the partition table to it allows us to change the layout in future versions of u-boot (almost independently of the kernel - there are still non-device tree kernels).
U-Boot becomes the single point of definition for all device tree kernels. Otherwise, each kernel (vendor vs. upstream + version) would ship its own partitioning. Moreover, u-boot has to know something about the partitioning, too, because it has to know where the environment is saved.
Disadvantages:
Users of the upstream linux kernel have to use a recent u-boot version to avoid the "black box" effect. A concrete impact is that the update routine (described/proposed by CompuLab) does not work out of the box with older u-boot versions.
Updating u-boot is something users might not want or miss to do.
However, I think nowadays it is ok to demand a recent u-boot in combination with the upstream kernel. The cm-fx6 wouldn't be the first board doing so. Hence, I propose these patches here.
Cheers, Christopher
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/434562.html [2] http://lists.denx.de/pipermail/u-boot/2016-June/258546.html