Re: [RFC PATCH] arm64: dts: qcom: add device tree for DB845c working in dual DSI mode

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 07/04/2023 19:48, Bjorn Andersson wrote:
> On Wed, Jan 18, 2023 at 08:47:53PM +0200, Dmitry Baryshkov wrote:
>> 18 января 2023 г. 19:32:42 GMT+02:00, Bjorn Andersson <andersson@kernel.org> пишет:
>>> On Wed, Jan 18, 2023 at 10:20:48AM +0200, Dmitry Baryshkov wrote:
>>>> While we are testing the DB845c working in dual DSI mode (which is
>>>> required for the 4k support), create a separate device tree using this
>>>> configuration.
>>>>
>>>
>>> I don't think it's right to change the DTB on your device depending on
>>> your TV's ability to do 4k or not...
>>>
>>> I ran into this problem when playing around with 4k-support on the RB3
>>> as well a while back. I was not able to figure out a way to run the
>>> lt9611 off two inputs for the lower resolutions and ended never posted
>>> anything because I couldn't come up with any good solution.
>>
>>
>> This is implemented with the latest lt9611 patchset, referenced in the patch annotation.
>>
>> I posted this as an RFC with the separate dts to let people test dual DSI, DPU wide planes, etc. and to compare that with plain old single link DSI/lt9611.
>>
>>>
>>>
>>> Would it be possible somehow to describe the two ports in DT, but have
>>> the display driver use one or both depending on the number of inputs
>>> needed by the lt9611?
>>
>> This would be very problemsome. Even switching the number of lanes
>> goes against the standard and is not supported by Linux kernel.
>> Supporting switching the host off and on would be a real troublle.
>>
> 
> Does this imply that switching resolution in runtime is not possible for
> any of these DSI->HDMI/DP/eDP bridges?
> 
> The immediate worry is that we need 4k and non-4k variants of every
> mezzanine (unless we start doing overlays). But beyond that I still
> don't like the fact that you need to change firmware depending on which
> monitor/TV you're going to connect the board to. (And with the current
> boot.img-based design, this is overly cumbersome)
No. With the latest lt9611 driver and with the current msm/msm-next it 
should not be necessary to have a separate dtsi. I submitted this patch 
as an RFC to let people compare 2xDSI vs single-link cases. Currently 
I'm happy with the way it works, so I can probably send this as a patch 
to main sdm845-db845c.dtb.

As a background info:
- lt9611 driver can utilize either one or two DSI links
- drm/msm can output 4k over two DSI links in bonded mode.
- drm/msm will still utilize two DSI links for smaller resolutions 
(switching between single and bonded DSI modes doesn't seem practical).
- If just one DSI link is supplied, 1080p is the maximum resolution that 
can be supported.


> Regards,
> Bjorn
> 
>> Hopefully, this is is not necessary.
>>
>>>
>>> Regards,
>>> Bjorn
>>>
>>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>>>> ---
>>>>
>>>> Dependencies to be able to verify the 4k@30 mode:
>>>> [1] https://lore.kernel.org/linux-arm-msm/20221229191856.3508092-1-dmitry.baryshkov@linaro.org/
>>>> [2] https://lore.kernel.org/dri-devel/20230118081658.2198520-1-dmitry.baryshkov@linaro.org/
>>>>
>>>> ---
>>>>   arch/arm64/boot/dts/qcom/Makefile             |  1 +
>>>>   .../boot/dts/qcom/sdm845-db845c-dual-dsi.dts  | 48 +++++++++++++++++++
>>>>   2 files changed, 49 insertions(+)
>>>>   create mode 100644 arch/arm64/boot/dts/qcom/sdm845-db845c-dual-dsi.dts
>>>>
>>>> diff --git a/arch/arm64/boot/dts/qcom/Makefile b/arch/arm64/boot/dts/qcom/Makefile
>>>> index 3e79496292e7..dc55c3b989a4 100644
>>>> --- a/arch/arm64/boot/dts/qcom/Makefile
>>>> +++ b/arch/arm64/boot/dts/qcom/Makefile
>>>> @@ -139,6 +139,7 @@ dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-cheza-r1.dtb
>>>>   dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-cheza-r2.dtb
>>>>   dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-cheza-r3.dtb
>>>>   dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-db845c.dtb
>>>> +dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-db845c-dual-dsi.dtb
>>>>   dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-db845c-navigation-mezzanine.dtb
>>>>   dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-lg-judyln.dtb
>>>>   dtb-$(CONFIG_ARCH_QCOM)	+= sdm845-lg-judyp.dtb
>>>> diff --git a/arch/arm64/boot/dts/qcom/sdm845-db845c-dual-dsi.dts b/arch/arm64/boot/dts/qcom/sdm845-db845c-dual-dsi.dts
>>>> new file mode 100644
>>>> index 000000000000..4a366dedc841
>>>> --- /dev/null
>>>> +++ b/arch/arm64/boot/dts/qcom/sdm845-db845c-dual-dsi.dts
>>>> @@ -0,0 +1,48 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Copyright (c) 2023, Linaro Ltd.
>>>> + */
>>>> +
>>>> +#include "sdm845-db845c.dts"
>>>> +
>>>> +&dsi0 {
>>>> +	qcom,dual-dsi-mode;
>>>> +	qcom,master-dsi;
>>>> +};
>>>> +
>>>> +&dsi1 {
>>>> +	vdda-supply = <&vreg_l26a_1p2>;
>>>> +
>>>> +	qcom,dual-dsi-mode;
>>>> +
>>>> +	/* DSI1 is slave, so use DSI0 clocks */
>>>> +	assigned-clock-parents = <&dsi0_phy 0>, <&dsi0_phy 1>;
>>>> +
>>>> +	status = "okay";
>>>> +
>>>> +	ports {
>>>> +		port@1 {
>>>> +			endpoint {
>>>> +				remote-endpoint = <&lt9611_b>;
>>>> +				data-lanes = <0 1 2 3>;
>>>> +			};
>>>> +		};
>>>> +	};
>>>> +};
>>>> +
>>>> +&dsi1_phy {
>>>> +	vdds-supply = <&vreg_l1a_0p875>;
>>>> +	status = "okay";
>>>> +};
>>>> +
>>>> +&lt9611_codec {
>>>> +	ports {
>>>> +		port@1 {
>>>> +			reg = <1>;
>>>> +
>>>> +			lt9611_b: endpoint {
>>>> +				remote-endpoint = <&dsi1_out>;
>>>> +			};
>>>> +		};
>>>> +	};
>>>> +};
>>>> -- 
>>>> 2.39.0
>>>>
>>

-- 
With best wishes
Dmitry