DRM MIPI DSI device and I2C device?

DRM MIPI DSI device and I2C device?

[Carsten Behling]

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Hi,

I would like to write a DRM bridge driver that is an I2C device and a DRM
MIPI DSI device.

It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their devices by
iterating over devicetree child nodes with for_each_available_child_of_node.

Since I can't make the bridge a child node of both, I don't know how to
resolve it.

Best regards
-Carsten

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Fwd: DRM MIPI DSI device and I2C device?

[Carsten Behling]

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> Hi,
>
> I would like to write a DRM bridge driver that is an I2C device and a DRM
MIPI DSI device.
>
> It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their devices by
iterating over devicetree child nodes with for_each_available_child_of_node.
>
>Since I can't make the bridge a child node of both, I don't know how to
resolve it.
>
Found the answer myself. adv7533 driver is a good example. Devicetree
exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI child
node.

> Best regards
>-Carsten

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Re: Fwd: DRM MIPI DSI device and I2C device?

[Laurent Pinchart]

Hi Carsten,

On Wednesday, 4 April 2018 11:41:05 EEST Carsten Behling wrote:
> > Hi,
> > 
> > I would like to write a DRM bridge driver that is an I2C device and a DRM
> > MIPI DSI device.
> > 
> > It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
> > 'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their devices by
> > iterating over devicetree child nodes with
> > for_each_available_child_of_node.
> > 
> > Since I can't make the bridge a child node of both, I don't know how to
> > resolve it.
> 
> Found the answer myself. adv7533 driver is a good example. Devicetree
> exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI child
> node.

This is an issue that has largely been ignored so far in Linux. Both DT and 
the Linux kernel device model organize devices in a tree structure based on 
the control buses. Devices that are connected to multiple control buses 
haven't been taken into account in the design and are thus hard to support.

As you may know, DSI can work in command mode or data mode. In data mode the 
DSI bus is only use to transfer video data, while in command mode it is also 
used to control the device (reading and writing registers).

A DSI device operating in data mode and controlled through I2C isn't a 
problem, as there's a single control bus in that case. The device should be a 
child of the I2C controller in DT, and will be instantiated through 
of_i2c_register_devices(). A DSI device operating in command mode without any 
other control bus isn't a problem either, it will be a child of the DSI master 
in DT, and will bee instantiated through mipi_dsi_host_register().

A DSI device operating in command mode that also require configuration through 
a separate control bus (such as I2C, but also SPI) is much more problematic to 
support. Fortunately those devices are rare. Hopefully your device won't fall 
in this category. If it does, we can discuss how to best support it.

-- 
Regards,

Laurent Pinchart



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Re: Fwd: DRM MIPI DSI device and I2C device?

[Andrzej Hajda]

On 05.04.2018 12:28, Laurent Pinchart wrote:
> Hi Carsten,
>
> On Wednesday, 4 April 2018 11:41:05 EEST Carsten Behling wrote:
>>> Hi,
>>>
>>> I would like to write a DRM bridge driver that is an I2C device and a DRM
>>> MIPI DSI device.
>>>
>>> It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
>>> 'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their devices by
>>> iterating over devicetree child nodes with
>>> for_each_available_child_of_node.
>>>
>>> Since I can't make the bridge a child node of both, I don't know how to
>>> resolve it.
>> Found the answer myself. adv7533 driver is a good example. Devicetree
>> exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI child
>> node.
> This is an issue that has largely been ignored so far in Linux. Both DT and 
> the Linux kernel device model organize devices in a tree structure based on 
> the control buses. Devices that are connected to multiple control buses 
> haven't been taken into account in the design and are thus hard to support.
>
> As you may know, DSI can work in command mode or data mode. In data mode the 
> DSI bus is only use to transfer video data, while in command mode it is also 
> used to control the device (reading and writing registers).

I am not sure what you mean by data and command mode. MIPI DSI specs
says about video and command mode - modes to transfer video data. In
both cases DSI can be used to control the device.

>
> A DSI device operating in data mode and controlled through I2C isn't a 
> problem, as there's a single control bus in that case. The device should be a 
> child of the I2C controller in DT, and will be instantiated through 
> of_i2c_register_devices(). 
> A DSI device operating in command mode without any 
> other control bus isn't a problem either, it will be a child of the DSI master 
> in DT, and will bee instantiated through mipi_dsi_host_register().
>
> A DSI device operating in command mode that also require configuration through 
> a separate control bus (such as I2C, but also SPI) is much more problematic to 
> support. Fortunately those devices are rare. Hopefully your device won't fall 
> in this category. If it does, we can discuss how to best support it.
>
As you have already found adv bridge is a good example. It is not clear
from the emails if DSI is used only to send video, or also to control?
And if to control, is it used to pass only specific commands

or can be used as alternative to i2c interface?


Regards

Andrzej



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Re: Fwd: DRM MIPI DSI device and I2C device?

[Laurent Pinchart]

Hi Andrzej,

On Thursday, 5 April 2018 14:28:51 EEST Andrzej Hajda wrote:
> On 05.04.2018 12:28, Laurent Pinchart wrote:
> > On Wednesday, 4 April 2018 11:41:05 EEST Carsten Behling wrote:
> >>> Hi,
> >>> 
> >>> I would like to write a DRM bridge driver that is an I2C device and a
> >>> DRM MIPI DSI device.
> >>> 
> >>> It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
> >>> 'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their devices
> >>> by iterating over devicetree child nodes with
> >>> for_each_available_child_of_node.
> >>> 
> >>> Since I can't make the bridge a child node of both, I don't know how to
> >>> resolve it.
> >> 
> >> Found the answer myself. adv7533 driver is a good example. Devicetree
> >> exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI child
> >> node.
> > 
> > This is an issue that has largely been ignored so far in Linux. Both DT
> > and the Linux kernel device model organize devices in a tree structure
> > based on the control buses. Devices that are connected to multiple control
> > buses haven't been taken into account in the design and are thus hard to
> > support.
> > 
> > As you may know, DSI can work in command mode or data mode. In data mode
> > the DSI bus is only use to transfer video data, while in command mode it
> > is also used to control the device (reading and writing registers).
> 
> I am not sure what you mean by data and command mode. MIPI DSI specs
> says about video and command mode - modes to transfer video data. In
> both cases DSI can be used to control the device.

Sorry, I meant pure video mode, when a panel only uses DSI to receive video 
data but handles all control communication through a separate control bus.

> > A DSI device operating in data mode and controlled through I2C isn't a
> > problem, as there's a single control bus in that case. The device should
> > be a child of the I2C controller in DT, and will be instantiated through
> > of_i2c_register_devices(). A DSI device operating in command mode without
> > any other control bus isn't a problem either, it will be a child of the
> > DSI master in DT, and will bee instantiated through
> > mipi_dsi_host_register().
> > 
> > A DSI device operating in command mode that also require configuration
> > through a separate control bus (such as I2C, but also SPI) is much more
> > problematic to support. Fortunately those devices are rare. Hopefully
> > your device won't fall in this category. If it does, we can discuss how
> > to best support it.
> 
> As you have already found adv bridge is a good example. It is not clear
> from the emails if DSI is used only to send video, or also to control?
> And if to control, is it used to pass only specific commands
> or can be used as alternative to i2c interface?

Carsten, could you please provide more information about the panel you're 
using ?

-- 
Regards,

Laurent Pinchart



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Re: Fwd: DRM MIPI DSI device and I2C device?

[Carsten Behling]

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> 2018-04-05 13:39 GMT+02:00 Laurent Pinchart <
laurent.pinchart@ideasonboard.com>:
> Hi Andrzej,
>
> On Thursday, 5 April 2018 14:28:51 EEST Andrzej Hajda wrote:
>> On 05.04.2018 12:28, Laurent Pinchart wrote:
>>> On Wednesday, 4 April 2018 11:41:05 EEST Carsten Behling wrote:
>>>>> Hi,
>>>>>
>>>>> I would like to write a DRM bridge driver that is an I2C device and a
>>>>> DRM MIPI DSI device.
>>>>>
>>>>> It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
>>>>> 'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their
devices
>>>>> by iterating over devicetree child nodes with
>>>>> for_each_available_child_of_node.
>>>>>
>>>>>> Since I can't make the bridge a child node of both, I don't know how
to
>>>>> resolve it.
>>>>
>>>> Found the answer myself. adv7533 driver is a good example. Devicetree
>>>> exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI
child
>>>> node.
>>>
>>> This is an issue that has largely been ignored so far in Linux. Both DT
>>> and the Linux kernel device model organize devices in a tree structure
>>> based on the control buses. Devices that are connected to multiple
control
>>> buses haven't been taken into account in the design and are thus hard to
>>> support.
>>>
>>> As you may know, DSI can work in command mode or data mode. In data mode
>>> the DSI bus is only use to transfer video data, while in command mode it
>>> is also used to control the device (reading and writing registers).
>>
>> I am not sure what you mean by data and command mode. MIPI DSI specs
>> says about video and command mode - modes to transfer video data. In
>> both cases DSI can be used to control the device.
>
> Sorry, I meant pure video mode, when a panel only uses DSI to receive
video
> data but handles all control communication through a separate control bus.
>
>>> A DSI device operating in data mode and controlled through I2C isn't a
>>> problem, as there's a single control bus in that case. The device should
>>> be a child of the I2C controller in DT, and will be instantiated through
>>> of_i2c_register_devices(). A DSI device operating in command mode
without
>>> any other control bus isn't a problem either, it will be a child of the
>>> DSI master in DT, and will bee instantiated through
>>> mipi_dsi_host_register().
>>>
>>> A DSI device operating in command mode that also require configuration
>>> through a separate control bus (such as I2C, but also SPI) is much more
>>> problematic to support. Fortunately those devices are rare. Hopefully
>>> your device won't fall in this category. If it does, we can discuss how
>>> to best support it.
>>
>> As you have already found adv bridge is a good example. It is not clear
>> from the emails if DSI is used only to send video, or also to control?
>> And if to control, is it used to pass only specific commands
>> or can be used as alternative to i2c interface?
>
>Carsten, could you please provide more information about the panel you're
>using ?

Sure, it's an TI SN65DSI84. It is just receiving pixel data on the input
lines.
I got an incomplete driver from Variscite that just writes a hardcoded  I2C
regmap from
DTS. I'm currently writing a real DRM bridge driver based on that. I didn't
find
a better one.

Regards
-Carsten

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Re: Fwd: DRM MIPI DSI device and I2C device?

[Andrzej Hajda]

On 05.04.2018 13:51, Carsten Behling wrote:
>
>
> > 2018-04-05 13:39 GMT+02:00 Laurent Pinchart
> <laurent.pinchart@ideasonboard.com
> <mailto:laurent.pinchart@ideasonboard.com>>:
> > Hi Andrzej,
> >
> > On Thursday, 5 April 2018 14:28:51 EEST Andrzej Hajda wrote:
> >> On 05.04.2018 12:28, Laurent Pinchart wrote:
> >>> On Wednesday, 4 April 2018 11:41:05 EEST Carsten Behling wrote:
> >>>>> Hi,
> >>>>>
> >>>>> I would like to write a DRM bridge driver that is an I2C device and a
> >>>>> DRM MIPI DSI device.
> >>>>>
> >>>>> It looks like that both - 'i2c-core.c: of_i2c_register_devices' and
> >>>>> 'drm_mipi_dsi.c: mipi_dsi_host_register'  are registering their devices
> >>>>> by iterating over devicetree child nodes with
> >>>>> for_each_available_child_of_node.
> >>>>>
> >>>>>> Since I can't make the bridge a child node of both, I don't know how to
> >>>>> resolve it.
> >>>>
> >>>> Found the answer myself. adv7533 driver is a good example. Devicetree
> >>>> exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI child
> >>>> node.
> >>>
> >>> This is an issue that has largely been ignored so far in Linux. Both DT
> >>> and the Linux kernel device model organize devices in a tree structure
> >>> based on the control buses. Devices that are connected to multiple
> control
> >>> buses haven't been taken into account in the design and are thus hard to
> >>> support.
> >>>
> >>> As you may know, DSI can work in command mode or data mode. In data mode
> >>> the DSI bus is only use to transfer video data, while in command mode it
> >>> is also used to control the device (reading and writing registers).
> >>
> >> I am not sure what you mean by data and command mode. MIPI DSI specs
> >> says about video and command mode - modes to transfer video data. In
> >> both cases DSI can be used to control the device.
> >
> > Sorry, I meant pure video mode, when a panel only uses DSI to
> receive video
> > data but handles all control communication through a separate
> control bus.
> >
> >>> A DSI device operating in data mode and controlled through I2C isn't a
> >>> problem, as there's a single control bus in that case. The device
> should
> >>> be a child of the I2C controller in DT, and will be instantiated
> through
> >>> of_i2c_register_devices(). A DSI device operating in command mode
> without
> >>> any other control bus isn't a problem either, it will be a child
> of the
> >>> DSI master in DT, and will bee instantiated through
> >>> mipi_dsi_host_register().
> >>>
> >>> A DSI device operating in command mode that also require configuration
> >>> through a separate control bus (such as I2C, but also SPI) is much
> more
> >>> problematic to support. Fortunately those devices are rare. Hopefully
> >>> your device won't fall in this category. If it does, we can
> discuss how
> >>> to best support it.
> >>
> >> As you have already found adv bridge is a good example. It is not clear
> >> from the emails if DSI is used only to send video, or also to control?
> >> And if to control, is it used to pass only specific commands
> >> or can be used as alternative to i2c interface?
> >
> >Carsten, could you please provide more information about the panel you're
> >using ?
>
> Sure, it's an TI SN65DSI84. It is just receiving pixel data on the
> input lines.
> I got an incomplete driver from Variscite that just writes a
> hardcoded  I2C regmap from
> DTS. I'm currently writing a real DRM bridge driver based on that. I
> didn't find
> a better one.

According to datasheet it looks like i2c controlled only DSI bridge, so
adv driver should be a good reference.

Regards
Andrzej

>
> Regards
> -Carsten
>

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