[U-Boot] [PATCH] arm: mx6: specify SPL padding

[Stefan Agner <stefan@agner.ch>]

On 2016-11-15 08:12, Tom Rini wrote:
> On Tue, Nov 15, 2016 at 09:59:22AM +0000, Max Krummenacher wrote:
>> Hi Stefan
>>
>> On Mon, 2016-11-14 at 18:06 -0800, Stefan Agner wrote:
>> > From: Stefan Agner <stefan.agner@toradex.com>
>> >
>> > When building SPL with eMMC boot support, specify standard padding
>> > for payload to match the load sector during boot. This allows to
>> > use the u-boot-with-spl.imx build target to generate a direcly
>> > flashable image which can be flashed using:
>> >
>> > ? dd if=u-boot-with-spl.imx of=/dev/mmcblk0 bs=512 skip=2
>> >
>> > Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
>> >
>> > ---
>> >
>> > ?include/configs/imx6_spl.h | 6 ++++++
>> > ?1 file changed, 6 insertions(+)
>> >
>> > diff --git a/include/configs/imx6_spl.h b/include/configs/imx6_spl.h
>> > index 76d1ca0..ca3ed19 100644
>> > --- a/include/configs/imx6_spl.h
>> > +++ b/include/configs/imx6_spl.h
>> > @@ -42,6 +42,12 @@
>> > ?#define CONFIG_SYS_MMCSD_FS_BOOT_PARTITION	1
>> > ?#define
>> > CONFIG_SYS_MONITOR_LEN??(CONFIG_SYS_U_BOOT_MAX_SIZE_SECTORS/2*1024)
>> > ?#define CONFIG_SPL_ABORT_ON_RAW_IMAGE
>> > +/*
>> > + * SPL starts at 1KB (ROM offset), hence we need to pad SPL up to
>> > 68KB so
>> > + * that payload (U-Boot) will be at 69KB (sector 138) on the eMMC/SD
>> > card.
>> > + * Required for targets such as u-boot-with-spl.imx.
>> > + */
>> > +#define CONFIG_SPL_PAD_TO			0x11000
>> > ?#endif
>> > ?
>> > ?/* SATA support */
>>
>> This has been brought up already:
>> https://www.mail-archive.com/u-boot at lists.denx.de/msg228246.html
>> I agreed with Marek that this might disrupt other boot sources
>> (NOR/SPI/ ...) which may or may not decide to use another offset
>> between SPL and U-Boot.
>> Thus it is advisable to move that define to the individual board
>> configuration where one knows for what boot device one wants to
>> use the combined u-boot-with-spl.imx binary.
> 
> I'm going to have to disagree with Marek here then.  Looking over the
> explanation in include/configs/imx6_spl.h we have:
> 1KiB up front "wasted" for a partition table
> 4KiB up next for the ROM-mandated header
> 64KiB for SPL itself, which is our max size, unconditionally set above
> this bit of context.  But it is the lowest common denominator in terms
> of IRAM size in the families.
> 
> Which brings us to the SPL_PAD_TO above, 68KiB.  We cannot go lower than
> this.  No one is changing any of this either today nor setting
> SPL_PAD_TO so
> u-boot-with-spl.imx isn't usable today.  None of this breaks using
> separate files.

I agree here, the pad seems pretty natural and should be usable across
boot devices. In fact, it probably should not be inside
CONFIG_SPL_MMC_SUPPORT, but at the top along with CONFIG_SPL_MAX_SIZE.

So far, include/config_fallbacks.h defined SPL_PAD_TO to 64KiB, which
renders u-boot-with-spl.imx unusable for SD/eMMC boot. Other boot
devices probably know a similar define (CONFIG_SYS_NAND_U_BOOT_OFFS).
Judging from existing board files it does not seem that anybody relied
on that 64kB padding so far... I guess if a board with a different boot
device wants to make use of u-boot-with-spl.imx, then it should make
sure that the offset is set correctly in its board file (e.g. using
#define CONFIG_SYS_NAND_U_BOOT_OFFS SPL_PAD_TO).

Marek?

--
Stefan