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

From: Alexandre Torgue
Date: Tue Apr 28 2020 - 04:40:15 EST

Hi Adrian

On 4/27/20 10:05 PM, Adrian Pop wrote:
Added lee.jones@xxxxxxxxxxx

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@xxxxxx> 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@xxxxxxxxx>
---

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@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