[U-Boot] [RESEND PATCH 3/3] sunxi: H6: use writel_relaxed for DRAM timing register accesses

[Alexander Graf]

On 02/10/2019 05:17 PM, Andre Przywara wrote:
> The timing registers in the DRAM controller can be programmed in any
> order, as they will only take effect once the controller is eventually
> "activated".
>
> Switch the MMIO writes in mctl_set_timing_lpddr3() over to use
> writel_relaxed(), since we don't need the stronger guarantee of the
> normal writel(). We satisfy the overall ordering requirement by ending
> the function with an explicit DMB barrier.
>
> In this case we are not interested in the performance benefit this
> usually gives, but in the saved instructions, which sum up for the many
> writes we have in the timing setup.
> Due to alignment effects this shrinks our chronically tight H6 SPL by a
> whopping 2KB, which brings it in the same region as for the other
> AArch64 Allwinner SPL builds.
>
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>

If you say it still works, it sounds like a pretty nifty optimization :).

Reviewed-by: Alexander Graf <agraf at suse.de>


Alex