[PATCH v4 08/10] rockchip: binman: Use the skip-at-start prop in simple-bin image

[Simon Glass]

Hi Quentin,

On Wed, 9 Apr 2025 at 07:35, Quentin Schulz <quentin.schulz at cherry.de> wrote:
>
> Hi Simon,
>
> On 4/9/25 3:33 PM, Simon Glass wrote:
> > Hi Quentin,
> >
> > On Wed, 9 Apr 2025 at 07:32, Quentin Schulz <quentin.schulz at cherry.de> wrote:
> >>
> >> Hi Simon,
> >>
> >> On 4/9/25 3:22 PM, Simon Glass wrote:
> >>> Hi Quentin,
> >>>
> >>> On Wed, 9 Apr 2025 at 04:57, Quentin Schulz <quentin.schulz at cherry.de> wrote:
> >>>>
> >>>> Hi Jonas, Simon,
> >>>>
> >>>> On 3/29/25 4:06 PM, Jonas Karlman wrote:
> >>>>> From: Simon Glass <sjg at chromium.org>
> >>>>>
> >>>>> The simple-bin image is normally written to MMC media at block 64, which
> >>>>> is a 32K offset from start of storage media.
> >>>>>
> >>>>> Set the skip-at-start property to 0x8000 (32 KiB) so that fdtmap and
> >>>>> other embedded binman symbols in the output binary is referencing image
> >>>>> offsets correctly.
> >>>>>
> >>>>
> >>>> Shouldn't we have this commit BEFORE we add the `fdtmap` node since we
> >>>> know it's wrong before this commit?
> >>>>
> >>>>> Signed-off-by: Simon Glass <sjg at chromium.org>
> >>>>> Signed-off-by: Jonas Karlman <jonas at kwiboo.se>
> >>>>> ---
> >>>>> Changes in v4:
> >>>>> - Drop defconfig changes
> >>>>> - Split from "VBE serial part H: Implement VBE on Rockchip RK3399"
> >>>>>
> >>>>> Changes in v2:
> >>>>> - Move this patch to the end of the series
> >>>>> - Drop 0x8000 offset for SPI
> >>>>> ---
> >>>>>     arch/arm/dts/rockchip-u-boot.dtsi | 3 ++-
> >>>>>     1 file changed, 2 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/arch/arm/dts/rockchip-u-boot.dtsi b/arch/arm/dts/rockchip-u-boot.dtsi
> >>>>> index fb38b7b80c43..65b81bf58626 100644
> >>>>> --- a/arch/arm/dts/rockchip-u-boot.dtsi
> >>>>> +++ b/arch/arm/dts/rockchip-u-boot.dtsi
> >>>>> @@ -154,6 +154,7 @@
> >>>>>         simple-bin {
> >>>>>                 filename = "u-boot-rockchip.bin";
> >>>>>                 pad-byte = <0xff>;
> >>>>> +             skip-at-start = <0x8000>;
> >>>>>
> >>>>>                 mkimage {
> >>>>>                         filename = "idbloader.img";
> >>>>> @@ -178,7 +179,7 @@
> >>>>>     #else
> >>>>>                 u-boot-img {
> >>>>>     #endif
> >>>>> -                     offset = <CONFIG_SPL_PAD_TO>;
> >>>>> +                     offset = <(CONFIG_SPL_PAD_TO + 0x8000)>;
> >>>>
> >>>> This is confusing. The documentation states:
> >>>>
> >>>> """
> >>>> offset:
> >>>>        This sets the offset of an entry within the image or section containing
> >>>>        it.
> >>>> """
> >>>>
> >>>> My understanding is that it should be relative to the beginning of the
> >>>> image but this now needs the knowledge of where it will be stored on the
> >>>> MMC device (via the value in skip-at-start).
> >>>>
> >>>> Why is skip-at-start automatically deducted from offset?
> >>>
> >>> This is how binman works[1]. We are trying to use the feature designs
> >>
> >> Why is it deducted?
> >
> > Are you asking why skip-at-start is deducted from the offset?
> >
>
> Yes

It is confusing, unfortunately.

When you use an offset (say 0x78000) then normally the entry will
start at that offset in the image.

When you use skip-at-start 0x8000, its value is added to all top-level
offsets in the image, so the offset becomes 0x80000

BUT the image built by binman does not contain the first 0x8000 bytes.
It is expected that the image is written to offset 0x8000 so that the
offsets will be correct when used within U-Boot itself.

Another way to think of it is that skip-at-start doesn't really change
any offsets; it just creates a hole at the start of the image. If you
didn't use skip-at-start you could manually set the first offset to
0x8000 and use dd to skip the first 0x8000 bytes when writing.

This feature was added for x86 to handle memory-mapped ROMs, but it
has proved useful for other cases now.

Regards,
Simon