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Subject: Re: [RFC PATCH v1 5/5] arm64: tegra: Add Tegra VI CSI suppport in
 device tree
From:   Sowjanya Komatineni <skomatineni@nvidia.com>
To:     Thierry Reding <thierry.reding@gmail.com>
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On 1/30/20 10:58 AM, Sowjanya Komatineni wrote:
>
> On 1/30/20 9:58 AM, Thierry Reding wrote:
>> On Thu, Jan 30, 2020 at 09:18:50AM -0800, Sowjanya Komatineni wrote:
>>> On 1/30/20 4:36 AM, Thierry Reding wrote:
>>>> On Wed, Jan 29, 2020 at 08:22:48AM -0800, Sowjanya Komatineni wrote:
>>>>> On 1/29/20 1:46 AM, Thierry Reding wrote:
>>>>>> On Tue, Jan 28, 2020 at 10:23:21AM -0800, Sowjanya Komatineni wrote:
>>>>>>> Tegra210 contains VI controller for video input capture from MIPI
>>>>>>> CSI camera sensors and also supports built-in test pattern=20
>>>>>>> generator.
>>>>>>>
>>>>>>> CSI ports can be one-to-one mapped to VI channels for capturing=20
>>>>>>> from
>>>>>>> an external sensor or from built-in test pattern generator.
>>>>>>>
>>>>>>> This patch adds support for VI and CSI and enables them in Tegra210
>>>>>>> device tree.
>>>>>>>
>>>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
>>>>>>> ---
>>>>>>> =A0=A0=A0 arch/arm64/boot/dts/nvidia/tegra210-p2597.dtsi | 8 ++++++=
+
>>>>>>> =A0=A0=A0 arch/arm64/boot/dts/nvidia/tegra210.dtsi=A0=A0=A0=A0=A0=
=A0 | 31=20
>>>>>>> +++++++++++++++++++++++++-
>>>>>>> =A0=A0=A0 2 files changed, 38 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/arch/arm64/boot/dts/nvidia/tegra210-p2597.dtsi=20
>>>>>>> b/arch/arm64/boot/dts/nvidia/tegra210-p2597.dtsi
>>>>>>> index b0095072bc28..ec1b3033fa03 100644
>>>>>>> --- a/arch/arm64/boot/dts/nvidia/tegra210-p2597.dtsi
>>>>>>> +++ b/arch/arm64/boot/dts/nvidia/tegra210-p2597.dtsi
>>>>>>> @@ -10,6 +10,14 @@
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 status =3D "okay";
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 };
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0 vi@54080000 {
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 status =3D "okay";
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0 };
>>>>>>> +
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0 csi@0x54080838 {
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 status =3D "okay";
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0 };
>>>>>>> +
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 sor@54580000 {
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 status =3D "okay";
>>>>>>> diff --git a/arch/arm64/boot/dts/nvidia/tegra210.dtsi=20
>>>>>>> b/arch/arm64/boot/dts/nvidia/tegra210.dtsi
>>>>>>> index 48c63256ba7f..c6107ec03ad1 100644
>>>>>>> --- a/arch/arm64/boot/dts/nvidia/tegra210.dtsi
>>>>>>> +++ b/arch/arm64/boot/dts/nvidia/tegra210.dtsi
>>>>>>> @@ -136,9 +136,38 @@
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 vi@54080000 {
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 compatible =3D "nvidi=
a,tegra210-vi";
>>>>>>> -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 reg =3D <0x0 0x54080000 0x0 0x00=
040000>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 reg =3D <0x0 0x54080000 0x0 0x80=
8>;
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 interrupts =3D <GIC_S=
PI 69 IRQ_TYPE_LEVEL_HIGH>;
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 status =3D "disabled"=
;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 assigned-clocks =3D <&tegra_car =
TEGRA210_CLK_VI>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 assigned-clock-parents =3D <&teg=
ra_car=20
>>>>>>> TEGRA210_CLK_PLL_C4_OUT0>;
>>>>>>> +
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 clocks =3D <&tegra_car TEGRA210_=
CLK_VI>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 clock-names =3D "vi";
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 resets =3D <&tegra_car 20>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 reset-names =3D "vi";
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0 };
>>>>>>> +
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0 csi@0x54080838 {
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 compatible =3D "nvidia,tegra210-=
csi";
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 reg =3D <0x0 0x54080838 0x0 0x20=
00>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 status =3D "disabled";
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 assigned-clocks =3D <&tegra_car =
TEGRA210_CLK_CILAB>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 <&=
tegra_car TEGRA210_CLK_CILCD>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 <&=
tegra_car TEGRA210_CLK_CILE>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 assigned-clock-parents =3D <&teg=
ra_car=20
>>>>>>> TEGRA210_CLK_PLL_P>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0 <&tegra_car TEGRA210_CLK_PLL_P>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0 <&tegra_car TEGRA210_CLK_PLL_P>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 assigned-clock-rates =3D <102000=
000>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0 <102000000>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0 <102000000>;
>>>>>>> +
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 clocks =3D <&tegra_car TEGRA210_=
CLK_CSI>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 <&tegra_car TEGRA=
210_CLK_CILAB>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 <&tegra_car TEGRA=
210_CLK_CILCD>,
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 <&tegra_car TEGRA=
210_CLK_CILE>;
>>>>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 clock-names =3D "csi", "cilab", =
"cilcd", "cile";
>>>>>>> +
>>>>>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 };
>>>>>> Can this be a child of the vi node? Looking at the register=20
>>>>>> ranges it
>>>>>> seems like these are actually a single IP block. If they have=20
>>>>>> separate
>>>>>> blocks with clearly separate functionality, then it makes sense=20
>>>>>> to have
>>>>>> CSI be a child node of VI, though it may also be okay to merge=20
>>>>>> both and
>>>>>> have a single node with the driver doing all of the differentiation
>>>>>> between what's VI and what's CSI.
>>>>>>
>>>>>> Looking at later chips, the split between VI and CSI is more=20
>>>>>> explicit,
>>>>>> so having the split in DT for Tegra210 may make sense for=20
>>>>>> consistency.
>>>>>>
>>>>>> I know we've discussed this before, but for some reason I keep=20
>>>>>> coming
>>>>>> back to this. I'll go through the other patches to see if I can=20
>>>>>> get a
>>>>>> clearer picture of how this could all work together.
>>>>>>
>>>>>> Thierry
>>>>> We can keep it separate as we discussed.
>>>>>
>>>>> But as Tegra186 onwards, CSI is separate device to be all=20
>>>>> cosistent I kept
>>>>> CSI as separate node for Tegra210 as well.
>>>> =A0 From our discussion, my understanding was that CSI would be a=20
>>>> separate
>>>> device, but it would still be a subdevice of VI. The address offset of
>>>> the CSI registers not being aligned to a power of two is a strong
>>>> indication that this is really all part of the same block.
>>> Yes our earlier discussion is to have CSI as subdevice.
>>>
>>> Later looking into T186 and later NVCSI is totally separate so it=20
>>> will be
>>> separate device and to have driver common moved Tegra210 CSI also as
>>> separate device instead of having it as subdevice of VI.
>>>
>>> Earlier when we discussed at that time I am using TPG also from device
>>> graphs but not moved to hard media links inside driver for TPG.
>>>
>>> For this we need CSI to be available prior to VI.
>> Why is that? Does creating the hard media links need access to a struct
>> device? What if we created that device in the VI driver without any
>> reliance on DT? Shouldn't that also work? I have a hard time imagining
>> that there aren't other devices like this where we don't necessarily
>> have separate devices for these links.
> Yes we need CSI structure for hard link TPG also as all csi channel=20
> list is part of CSI device.
>
> We can create CSI channel subdevices within VI without using CSI=20
> device from a separate CSI driver probe for Tegra210 and make all=20
> subdev related ops implementations as global so they can be used from=20
> VI driver for Tegra210 and can also be used for Tegra186 and later in=20
> separate CSI driver.
>
> During creating media links in VI driver for TPG, for T210 we can use=20
> local CSI device structure and for T186+ we can use CSI device=20
> structure created during CSI probe.
>
> Sorry, I didn't understood what you meant by separate devices for=20
> these link.
>
> We only have Tegra CSI linked to Tegra VI for TPG/Real sensor.
>
>>> If we add CSI as subdevice to VI, CSI will not be available by the time
>>> VI init happens.
>> The CSI subdevice should be registered as part of the VI driver's probe,
>> right? That's typically where you'd call of_platform_populate(). Could
>> we not set up the hard media links in the ->init() callbacks for the
>> host1x clients? Those are called after all of the devices have been
>> probed, so the CSI device should be available at that time.
>>
yes, will update to have CSI as child node to VI
>>> Currently host1x subdevices listed has CSI before VI and CSI init=20
>>> happens
>>> earlier so by the time VI init happens CSI is available to do media=20
>>> links
>>> b/w VI video entity and CSI subdevice entity.
>> Okay, I understand how this would be a convenient solution. However, the
>> device tree is a hardware description, so we need to ignore what we know
>> about the operating system infrastructure that we want to use when
>> writing the device tree bindings (and the device tree content) in order
>> to make sure the same binding will work on a different operating system
>> which may have a completely different infrastructure (or none at all).
>>
>>> Also having CSI as separate subdevice (not as subdevice to VI) for=20
>>> T210 will
>>> be consistent with T186 and later.
>> Again, I see how that's convenient. But the main difference between
>> Tegra210 and Tegra186 is that on the former, the CSI is merged with VI,
>> whereas on the latter the CSI is a completely separate hardware block.
>>
>> Since device tree describes the hardware, that difference should be
>> apparent in the device tree. I initially thought as well that it would
>> be advantageous if both had the same representation, but I do realize
>> now that this has a significant impact on the device tree, and it
>> violates the basic principles we base device tree binding design on.
>>
>> Thierry
>
> I just thought of driver implementation being common b/w T210 and=20
> T186+ by having CSI as separate device node rather than as child node=20
> to VI to avoid CSI structure handling within VI for T210 only.
>
> Will update DT and driver to have CSI as child node of VI for T210.
>
>