linux-kernel - Re: [PATCH RFC 4/6] ARM: dts: msm8974: add display support

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Date:   Thu, 9 May 2019 07:59:12 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Brian Masney <masneyb@...tation.org>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH RFC 4/6] ARM: dts: msm8974: add display support

On Thu 09 May 00:12 PDT 2019, Brian Masney wrote:

> On Wed, May 08, 2019 at 08:00:47PM -0700, Bjorn Andersson wrote:
> > On Wed 08 May 19:25 PDT 2019, Rob Clark wrote:
> > 
> > > On Wed, May 8, 2019 at 7:16 PM Brian Masney <masneyb@...tation.org> wrote:
> > > >
> > > > On Mon, May 06, 2019 at 11:39:02PM -0700, Bjorn Andersson wrote:
> > > > > On Sun 05 May 06:04 PDT 2019, Brian Masney wrote:
> > > > > > diff --git a/arch/arm/boot/dts/qcom-msm8974.dtsi b/arch/arm/boot/dts/qcom-msm8974.dtsi
> > > > > [..]
> > > > > > +                           clocks = <&mmcc MDSS_MDP_CLK>,
> > > > > > +                                    <&mmcc MDSS_AHB_CLK>,
> > > > > > +                                    <&mmcc MDSS_AXI_CLK>,
> > > > > > +                                    <&mmcc MDSS_BYTE0_CLK>,
> > > > > > +                                    <&mmcc MDSS_PCLK0_CLK>,
> > > > > > +                                    <&mmcc MDSS_ESC0_CLK>,
> > > > > > +                                    <&mmcc MMSS_MISC_AHB_CLK>;
> > > > > > +                           clock-names = "mdp_core",
> > > > > > +                                         "iface",
> > > > > > +                                         "bus",
> > > > > > +                                         "byte",
> > > > > > +                                         "pixel",
> > > > > > +                                         "core",
> > > > > > +                                         "core_mmss";
> > > > >
> > > > > Unless I enable MMSS_MMSSNOC_AXI_CLK and MMSS_S0_AXI_CLK I get some
> > > > > underrun error from DSI. You don't see anything like this?
> > > > >
> > > > > (These clocks are controlled by msm_bus downstream and should be driven
> > > > > by interconnect upstream)
> > > > >
> > > > >
> > > > > Apart from this, I think this looks nice. Happy to see the progress.
> > > >
> > > > No, I'm not seeing an underrun errors from the DSI. I think the clocks
> > > > are fine since I'm able to get this working with 4.17 using these same
> > > > clocks. I just sent out v2 and the cover letter has some details, along
> > > > with the full dmesg.
> > > 
> > > since we don't have interconnect driver for 8974, I guess there is
> > > some chance that things work or not based on how lk leaves things?
> > > 
> > 
> > Right, I guess the bootloader on my device does not leave the busses
> > ticking - perhaps there's a boot splash involved on Brian's device?
> > 
> > Regardless, this works on Nexus 5 and allows Brian to make further
> > progress so I'm all for merging it.
> 
> There is a boot splash on the Nexus 5 and that may explain a behavior
> that I observed. I attempted to add reset GPIO support to the simple
> panel driver and the screen will clear but nothing will come on the
> screen after a hard reset, even on 4.17. To be sure, I got the timing
> information for how long to leave the GPIO high and low from the
> downstream MSM 3.4 sources. That's when I had a script port all of the
> ~400 panel on commands in the downstream device tree to a new panel
> driver.
> 
> With the latest kernel kernel having a delay showing the console text,
> I observe a brief second where the boot splash is shown along with the
> startup text from Linux. A full refresh is performed and the boot
> splash goes away. I don't see this with the 4.17 kernel; perhaps maybe
> the full refresh occurs quick enough that its not noticeable.
> 
> Can you point me to where the interconnect API is in the downstream
> MSM 3.4 sources? https://github.com/AICP/kernel_lge_hammerhead
> It looks like its in drivers/interconnect/ in the upstream sources.
> 

The data will be 8974 specific, but the plumbing should be reusable from
8916 or 404. Hopefully we can get those landed shortly.

You can find the latest incarnation here:
https://lore.kernel.org/lkml/20190415104357.5305-1-georgi.djakov@linaro.org/

Regards,
Bjorn