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From:   Adrian Pop <pop.adrian61@gmail.com>
Date:   Mon, 27 Apr 2020 23:05:54 +0300
Message-ID: <CAP-HsdS0rq4iCq1oqpTU=EXF8UWbfPivCJVZG-4b7jyvdHHXUw@mail.gmail.com>
Subject: Re: [PATCH 2/2] arm: dts: stm32f769-disco: Enable MIPI DSI display support
To:     Alexandre Torgue <alexandre.torgue@st.com>,
        Lee Jones <lee.jones@linaro.org>
Cc:     Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Added lee.jones@linaro.org.

First, thank you all for taking a look at my changes!

Hello Alex,

On Mon, Apr 27, 2020 at 11:28 AM Alexandre Torgue
<alexandre.torgue@st.com> wrote:
>
> Hi Adrian
>
> On 4/24/20 8:21 PM, Adrian Pop wrote:
> > STM32f769-disco features a 4" MIPI DSI display: add support for it.
> >
> > Signed-off-by: Adrian Pop <pop.adrian61@gmail.com>
> > ---
>
> Commit title should be ARM: dts: stm32: ...

Will fix in next version if that's ok.

>
> Can you explain a bit more in your commit message why do you use a
> reserved memory pool for DMA and where this pool is located. (I assume
> it's linked to a story of DMA and cache memory attribute on cortexM7...)

Need to look more into this, but if I remove it, /dev/fb0 is not
available anymore and I get a warning stating:
...
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] Initialized stm 1.0.0 20170330 for 40016800.display-controller on minor 0
------------[ cut here ]------------
WARNING: CPU: 0 PID: 13 at arch/arm/mm/dma-mapping-nommu.c:50 0xc000b8ed
CPU: 0 PID: 13 Comm: kworker/0:1 Not tainted 5.6.0-next-20200412 #23
Hardware name: STM32 (Device Tree Support)
Workqueue: events 0xc014fa35
Function entered at [<c000b325>] from [<c000a487>]
...

When I looked in arch/arm/mm/dma-mapping-nommu.c:50, there is a comment stating:

    /*
     * dma_alloc_from_global_coherent() may fail because:
     *
     * - no consistent DMA region has been defined, so we can't
     *   continue.
     * - there is no space left in consistent DMA region, so we
     *   only can fallback to generic allocator if we are
     *   advertised that consistency is not required.
     */

This is the reason I added the reserved-memory.

About the location, does it need to be hardcoded? On my board
(STM32F769I-Disco, tftp boot) in boot log I get:
...
Reserved memory: created DMA memory pool at 0xc0ef1000, size 1 MiB
OF: reserved mem: initialized node linux,dma, compatible id shared-dma-pool
...

>
> Did you try this configuration with XIP boot ?

I did not try with XIP. Currently loading zImage from tftp to memory.
Will try with XIP as well, and get back with feedback.

>
> regards
> alex
>
> >   arch/arm/boot/dts/stm32f746.dtsi      | 34 ++++++++++++++++++
> >   arch/arm/boot/dts/stm32f769-disco.dts | 50 +++++++++++++++++++++++++++
> >   2 files changed, 84 insertions(+)
> >
> > diff --git a/arch/arm/boot/dts/stm32f746.dtsi b/arch/arm/boot/dts/stm32f746.dtsi
> > index 93c063796780..202bb6edc9f1 100644
> > --- a/arch/arm/boot/dts/stm32f746.dtsi
> > +++ b/arch/arm/boot/dts/stm32f746.dtsi
> > @@ -48,6 +48,19 @@ / {
> >       #address-cells = <1>;
> >       #size-cells = <1>;
> >
> > +     reserved-memory {
> > +             #address-cells = <1>;
> > +             #size-cells = <1>;
> > +             ranges;
> > +
> > +             linux,dma {
> > +                     compatible = "shared-dma-pool";
> > +                     linux,dma-default;
> > +                     no-map;
> > +                     size = <0x10F000>;
> > +             };
> > +     };
> > +
> >       clocks {
> >               clk_hse: clk-hse {
> >                       #clock-cells = <0>;
> > @@ -75,6 +88,27 @@ clk_i2s_ckin: clk-i2s-ckin {
> >       };
> >
> >       soc {
> > +             ltdc: display-controller@40016800 {
> > +                     compatible = "st,stm32-ltdc";
> > +                     reg = <0x40016800 0x200>;
> > +                     interrupts = <88>, <89>;
> > +                     resets = <&rcc STM32F7_APB2_RESET(LTDC)>;
> > +                     clocks = <&rcc 1 CLK_LCD>;
> > +                     clock-names = "lcd";
> > +                     status = "disabled";
> > +             };
> > +
> > +             dsi: dsi@40016c00 {
> > +                     compatible = "st,stm32-dsi";
> > +                     reg = <0x40016c00 0x800>;
> > +                     interrupts = <98>;
> > +                     clocks = <&rcc 1 CLK_F769_DSI>, <&clk_hse>;
> > +                     clock-names = "pclk", "ref";
> > +                     resets = <&rcc STM32F7_APB2_RESET(DSI)>;
> > +                     reset-names = "apb";
> > +                     status = "disabled";
> > +             };
> > +
> >               timer2: timer@40000000 {
> >                       compatible = "st,stm32-timer";
> >                       reg = <0x40000000 0x400>;
> > diff --git a/arch/arm/boot/dts/stm32f769-disco.dts b/arch/arm/boot/dts/stm32f769-disco.dts
> > index 1626e00bb2cb..30ebbc193e82 100644
> > --- a/arch/arm/boot/dts/stm32f769-disco.dts
> > +++ b/arch/arm/boot/dts/stm32f769-disco.dts
> > @@ -153,3 +153,53 @@ &usbotg_hs {
> >       pinctrl-names = "default";
> >       status = "okay";
> >   };
> > +
> > +&dsi {
> > +     #address-cells = <1>;
> > +     #size-cells = <0>;
> > +     status = "okay";
> > +
> > +     ports {
> > +             #address-cells = <1>;
> > +             #size-cells = <0>;
> > +
> > +             port@0 {
> > +                     reg = <0>;
> > +                     dsi_in: endpoint {
> > +                             remote-endpoint = <&ltdc_out_dsi>;
> > +                     };
> > +             };
> > +
> > +             port@1 {
> > +                     reg = <1>;
> > +                     dsi_out: endpoint {
> > +                             remote-endpoint = <&dsi_in_panel>;
> > +                     };
> > +             };
> > +
> > +     };
> > +
> > +     panel: panel {
> > +             compatible = "orisetech,otm8009a";
> > +             reg = <0>; /* dsi virtual channel (0..3) */
> > +             reset-gpios = <&gpioj 15 GPIO_ACTIVE_LOW>;
> > +             status = "okay";
> > +
> > +             port {
> > +                     dsi_in_panel: endpoint {
> > +                             remote-endpoint = <&dsi_out>;
> > +                     };
> > +             };
> > +     };
> > +};
> > +
> > +&ltdc {
> > +     dma-ranges;

Need to remove this, not needed and causes a warning.

> > +     status = "okay";
> > +
> > +     port {
> > +             ltdc_out_dsi: endpoint {
> > +                     remote-endpoint = <&dsi_in>;
> > +             };
> > +     };
> > +};
> >

Regards,
Adrian