linux-kernel - Re: [PATCH 2/2] arm: dts: stm32f769-disco: Enable MIPI DSI display support

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Date:   Tue, 28 Apr 2020 10:39:42 +0200
From:   Alexandre Torgue <alexandre.torgue@...com>
To:     Adrian Pop <pop.adrian61@...il.com>,
        Lee Jones <lee.jones@...aro.org>
CC:     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

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 ?



> 
> 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.

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
>