[PATCH v2 3/6] video: broadwell: Use mtrr_set_next_var() for graphics memory

[Simon Glass]

On Mon, 31 Jul 2023 at 00:03, Bin Meng <bmeng at tinylab.org> wrote:
>
> From: Bin Meng <bmeng.cn at gmail.com>
>
> At present this uses mtrr_add_request() & mtrr_commit() combination
> to program the MTRR for graphics memory. This usage has two major
> issues as below:
>
> - mtrr_commit() will re-initialize all MTRR registers from index 0,
>   using the settings previously added by mtrr_add_request() and saved
>   in gd->arch.mtrr_req[], which won't cause any issue but is unnecessary
> - The way such combination works is based on the assumption that U-Boot
>   has full control with MTRR programming (e.g.: U-Boot without any blob
>   that does all low-level initialization on its own, or using FSP2 which
>   does not touch MTRR), but this is not the case with FSP. FSP programs
>   some MTRRs during its execution but U-Boot does not have the settings
>   saved in gd->arch.mtrr_req[] and when doing mtrr_commit() it will
>   corrupt what was already programmed previously.
>
> Correct this to use mtrr_set_next_var() instead.
>
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> ---
>
> (no changes since v1)
>
>  drivers/video/broadwell_igd.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)

Reviewed-by: Simon Glass <sjg at chromium.org>