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Date:   Sat, 16 May 2020 11:39:03 +0300
From:   Adrian Pop <pop.adrian61@...il.com>
To:     Alexandre Torgue <alexandre.torgue@...com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm: dts: stm32f769-disco: Enable MIPI DSI display support

 Hello all,

a bit of a delayed response here, but:

On Tue, Apr 28, 2020 at 11:39 AM Alexandre Torgue
<alexandre.torgue@...com> wrote:
>
> Hi Adrian
>
> On 4/27/20 10:05 PM, Adrian Pop wrote:
> > Added lee.jones@...aro.org.
> >
> > First, thank you all for taking a look at my changes!
>
> no pb.
>
> >
> > Hello Alex,
> >
> > On Mon, Apr 27, 2020 at 11:28 AM Alexandre Torgue
> > <alexandre.torgue@...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@...il.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.
>
> Note that on cortexM7 DMA can't use cached memory. For this reason you
> have to declare a dedicated memory area for DMA with no-cache attribute.
> It is done thanks to a "linux,dma" node plus a kernel config:
> CONFIG_ARM_MPU. I planed to declare this dedicated memeory region in
> sram. Can you check if add it for the same reason I explain and check if
> it works using sram ?
>

I did not have CONFIG_ARM_MPU enabled, enabled it now.

Just tried with SRAM:
reg = <0x20020000 0x60000>; /* SRAM1 368KB + SRAM2 16KB*/

but `arm_nommu_dma_alloc()` size parameter is 819200 (which is bigger
than the SRAM reserved memory), so the
`dma_alloc_from_global_coherent()` fails, so again I get the warning
stated above.

>
>
> >
> > 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.

Still trying to figure how to XIP :).

>
> Ok thanks.
>
> >
> >>
> >> 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@...16800 {
> >>> +                     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@...16c00 {
> >>> +                     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@...00000 {
> >>>                        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
> >

Regards,
Adrian

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