[U-Boot] [PATCH 8/8] x86: quark: Optimize MRC execution time

[Simon Glass]

Hi Bin,

On 31 August 2015 at 03:52, Bin Meng <bmeng.cn at gmail.com> wrote:
> Boot time performance degradation is observed with the conversion
> to use dm pci. Intel Quark SoC has a low end x86 processor with
> only 400MHz frequency and the most time consuming part is with MRC.
> Each MRC register programming requires indirect access via pci bus.
> With dm pci, accessing pci configuration space has some overhead.
> Unfortunately this single access overhead gets accumulated in the
> whole MRC process, and finally leads to twice boot time (25 seconds)
> than before (12 seconds).
>
> To speed up the boot, create an optimized version of pci config
> read/write routines without bothering to go through driver model.
> Now it only takes about 3 seconds to finish MRC, which is really
> fast (8 times faster than dm pci, or 4 times faster than before).
>
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> ---
>
>  arch/x86/cpu/quark/msg_port.c | 59 +++++++++++++++++++++++++++----------------
>  1 file changed, 37 insertions(+), 22 deletions(-)

Before I delve into the patch - with driver model we are using the I/O
method - see pci_x86_read_config(). Is that the source of the slowdown
or is it just general driver model overhead.

If the former then perhaps we should change this. If the latter then
we have work to do...

Regards,
Simon