Re: [PATCH] arm64: dts: qcom: sc7180: Modify SPI_CLK voltage level for trogdor

[Doug Anderson]

Bjorn,

On Mon, May 10, 2021 at 7:53 AM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> From: Wenchao Han <hanwenchao@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
>
> On coachz it could be observed that SPI_CLK voltage level was only
> 1.4V during active transfers because the drive strength was too
> weak. The line hadn't finished slewing up by the time we started
> driving it down again. Using a drive strength of 8 lets us achieve the
> correct voltage level of 1.8V.
>
> Though the worst problems were observed on coachz hardware, let's do
> this across the board for trogdor devices. Scoping other boards shows
> that this makes the clk line look nicer on them too and doesn't
> introduce any problems.
>
> Only the clk line is adjusted, not any data lines. Because SPI isn't a
> DDR protocol we only sample the data lines on either rising or falling
> edges, not both. That means the clk line needs to toggle twice as fast
> as data lines so having the higher drive strength is more important
> there.
>
> Signed-off-by: Wenchao Han <hanwenchao@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
> [dianders: Adjust author real name; adjust commit message]
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
>
>  arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 1 +
>  1 file changed, 1 insertion(+)

I think this patch is ready to land and it's what we're now using in
the Chrome OS tree. See <https://crrev.com/c/2821728>.

-Doug