On 07/31/2014 04:03 PM, Simon Glass wrote:
Hi Stephen,
On 30 July 2014 23:37, Stephen Warren swarren@wwwdotorg.org wrote:
From: Dennis Gilmore dennis@ausil.us
This generic $bootcmd, and associated support macros, automatically searches a defined set of storage devices (or network protocols) for an extlinux configuration file or U-Boot boot script in various standardized locations. Distros that install such a boot config file/script in those standard locations will get easy-to-set-up booting on HW that enables this generic $bootcmd.
Boards can define the set of devices from which boot is attempted, and the order in which they are attempted. Users may later customize this set/order by edting $boot_targets.
Users may interrupt the boot process and boot from a specific device simply by executing e.g.:
$ run bootcmd_mmc1 or: $ run bootcmd_pxe
This patch was originally written by Dennis Gilmore based on Tegra and rpi_b boot scripts. I have made the following modifications since then:
Boards must define the BOOT_TARGET_DEVICES macro in order to specify the set of devices (and order) from which to attempt boot. If needed, we can define a default directly in config_distro_bootcmd.h.
Removed $env_import and related variables; nothing used them, and I think it's better for boards to pre-load an environment customization file using CONFIG_PREBOOT if they need.
Renamed a bunch of variables to suit my whims:-)
Signed-off-by: Dennis Gilmore dennis@ausil.us Signed-off-by: Stephen Warren swarren@nvidia.com
I do understand the desirability of getting something sorted in this area. But I am not thrilled with all the macro magic. How does this fit with the new Kconfig setup? It encourages a single setting for each variable, and I feel that the #ifdefs are not compatible with that.
I think Kconfig would be completely unsuitable for this kind of detailed configuration. Kconfig is great for enabling/disabling features, but applying it here feels too much to me. Equally, Kconfig is rather new in U-Boot. It'd be better to enable the feature so that distros can rely on it, and then refactor it later if required.
I do feel that actually implementing the boot script as U-Boot environment variables is much preferred over hard-coding any algorithm into U-Boot. That way, the user can easily modify the scripts as they desire. If we just put e.g. $boot_targets into the environment or DT, but none of the other scripts in this patch, the user would be much more severely restricted in how they could reconfigure the system to act how they want.
Would it be possible to put the settings in the device tree somehow instead of CONFIGs?
At least part of the information isn't a HW description, but rather user-/vendor configuration. So, I don't think it's appropriate to put this into DT. Equally, very few U-Boot platforms currently use DT, and I certainly hope it doesn't become mandatory in any way. So, using DT for this purpose would severely limit the platforms where this feature was available.
I did send a series some time ago that aimed to improve the default environment specification in config files - it was parked while Kconfig was going on, but we could revisit it.
I think we'd still need to use a C pre-processor (or some other code generation/templating tool) even with that scheme in place. So, I think the two are orthogonal.