imx8m-mini csi-2 limitations

imx8m-mini csi-2 limitations

[Petko Manolov]

	Hello guys,

I'm developing a driver for Sony imx492 sensor and i'm using imx8m-mini
(Variscite SoM on Symphony carrier board) platform.  Thanks to Laurent i dumped
the vendor mipi-csi and csi-bridge drivers in favor of mainline (v5.19-rc6 atm)
and parts started to click in place.  However, there are still a few rough
edges.

The sensor is 47mpix, and is only capable of streaming over all four CSI-2
lanes.  Each lane is 1.728gbit, which makes 6.912gbps total bandwidth.
imx8m-mini's d-phy can handle (on paper) up to 6gbps.

I guess the main question here is: what's the fastest transfer rate that's known
to work with this SoC?  Does anyone have experience with imx8m-mini in this
regard?


Even with the settings that i'm able to obtain a (distorted) test pattern image
with, i keep getting tons of:

[99910.847591] imx-mipi-csis 32e30000.mipi-csi: FIFO Overflow Error events: 1353347

IRQs also look a suspicious on the 'csi' part:

214:    2653716          0          0          0     GICv3  49 Level     32e30000.mipi-csi
215:          2          0          0          0     GICv3  48 Level     csi

That's with this clock setup:

 sys_pll2                             1        1        0  1000000000          0     0  50000         Y
    sys_pll2_out                      5        5        0  1000000000          0     0  50000         Y
       sys_pll2_1000m                 3        3        0  1000000000          0     0  50000         Y
          csi1_phy_ref                1        1        0  1000000000          0     0  50000         Y
          csi1_core                   1        1        0   500000000          0     0  50000         Y
             csi1_root_clk            1        1        0   500000000          0     0  50000         Y

However, if i change the latter two (csi1_core & csi1_root_clk) to 1ghz, there
are still mipi-csi IRQs coming in, but nothing from the csi-bridge.

Any advice on where i shall start looking first?


thanks,
Petko

Re: imx8m-mini csi-2 limitations

[Petko Manolov]

	Hello again,

After digging down NXP's documentation and reading some comments within kernel 
drivers (sorry Jacopo, you've left some nice comments in imx7-media-csi.c, hence 
you're spammed now :) i came to the conclusion that mipi-csi to csi-bridge data 
path can only be 8bits in raw12 format.  The only exception is YUV422 format, 
which get BIT_MIPI_DOUBLE_CMPNT flag set.

So i guess there are two questions:

	a) can the csi-bridge (and mipi-csi) be persuaded to do two-bytes for 
	raw12 format;

	b) what's the maximum frequency for csi-bridge PIXCLK?

I've increased PIXCLK up to 1ghz (as opposed to the default 500mhz) and this seem 
to hung the bridge.


cheers,
Petko


On 22-08-15 16:52:59, Petko Manolov wrote:
> 	Hello guys,
> 
> I'm developing a driver for Sony imx492 sensor and i'm using imx8m-mini
> (Variscite SoM on Symphony carrier board) platform.  Thanks to Laurent i dumped
> the vendor mipi-csi and csi-bridge drivers in favor of mainline (v5.19-rc6 atm)
> and parts started to click in place.  However, there are still a few rough
> edges.
> 
> The sensor is 47mpix, and is only capable of streaming over all four CSI-2
> lanes.  Each lane is 1.728gbit, which makes 6.912gbps total bandwidth.
> imx8m-mini's d-phy can handle (on paper) up to 6gbps.
> 
> I guess the main question here is: what's the fastest transfer rate that's known
> to work with this SoC?  Does anyone have experience with imx8m-mini in this
> regard?
> 
> 
> Even with the settings that i'm able to obtain a (distorted) test pattern image
> with, i keep getting tons of:
> 
> [99910.847591] imx-mipi-csis 32e30000.mipi-csi: FIFO Overflow Error events: 1353347
> 
> IRQs also look a suspicious on the 'csi' part:
> 
> 214:    2653716          0          0          0     GICv3  49 Level     32e30000.mipi-csi
> 215:          2          0          0          0     GICv3  48 Level     csi
> 
> That's with this clock setup:
> 
>  sys_pll2                             1        1        0  1000000000          0     0  50000         Y
>     sys_pll2_out                      5        5        0  1000000000          0     0  50000         Y
>        sys_pll2_1000m                 3        3        0  1000000000          0     0  50000         Y
>           csi1_phy_ref                1        1        0  1000000000          0     0  50000         Y
>           csi1_core                   1        1        0   500000000          0     0  50000         Y
>              csi1_root_clk            1        1        0   500000000          0     0  50000         Y
> 
> However, if i change the latter two (csi1_core & csi1_root_clk) to 1ghz, there
> are still mipi-csi IRQs coming in, but nothing from the csi-bridge.
> 
> Any advice on where i shall start looking first?
> 
> 
> thanks,
> Petko

Re: imx8m-mini csi-2 limitations

[Jacopo Mondi]

Hi Petko

On Thu, Aug 18, 2022 at 12:27:45PM +0300, Petko Manolov wrote:
> 	Hello again,
>
> After digging down NXP's documentation and reading some comments within kernel
> drivers (sorry Jacopo, you've left some nice comments in imx7-media-csi.c, hence
> you're spammed now :) i came to the conclusion that mipi-csi to csi-bridge data

No worries.

I tried re-reading all the discussions, but memory still fails me
here.

I recall I had an issue with the CSIS bandwidth and somewhere I
suggested that it might be due to the CSI-2 specification version that
the peripheral implemented. I can't find that email anymore though :/

> path can only be 8bits in raw12 format.  The only exception is YUV422 format,
> which get BIT_MIPI_DOUBLE_CMPNT flag set.
>

Yes, there has been quite some discussions about how to mix-and-match
the settings between the CSIS (mipi-csi) and the CSI (csi-bridge) [*]

If I recall correctly there are at least three configurations at play:

- The CSIS pixel mode selection

  MIPI_CSI_ISP_CONFIG[13:12]

  The driver currently forces dual pixel sampling mode for YUV422
  and report a TODO:

  * TODO: Verify which other formats require DUAL (or QUAD) modes.

  Here you're trying to transfer RAW12 data, which is indicated in the
  register documentation as one of the formats suitable for DUAL/QUAD
  mode transfer

  - I'm actually not sure how and if RAW12 gets expanded to 16 bit
    samples by filling the 16-bit word with 0s or it either gets
    packed in 6 bytes with no paddings. Figure "13-33. Pixel
    alignment" seems to suggest that, but I'm not sure I really got
    that diagram

- The CSI-bridge

  - CSI_CR3[3] SENSOR_16BITS
  - CSI_CR18[20] MIPI_DOUBLE_CMP

  The comment in imx7_csi_configure() explains how different versions
  of YUYV (2X8 and 1X16) are handled, and why SENSOR_16BITS and
  MIPI_DOUBLE_CMP have to be enabled when the csi-bridge has to be instructed
  to sample 16 bits samples from the RX queue.

I guess the key would be here to find out what combination of
SINGLE/DUAL/QUAD sampling is opportune for RAW12 (I would try with
DUAL first and then QUAD) and then configure the csi-bridge bus
sampling mode accordingly (likely in the same was as it is done for
YUYV_1X16)

When it comes to bandwidth limitation, can you try to reduce the
sensor output size to make sure you chase one issue at the time ?

[*] Is "CSI" the most abused acronym of history ?

> So i guess there are two questions:
>
> 	a) can the csi-bridge (and mipi-csi) be persuaded to do two-bytes for
> 	raw12 format;

See above :)

> 	b) what's the maximum frequency for csi-bridge PIXCLK?
>

Not sure about this one.

I've anyway cc-ed Laurent and Xavier, which can surely be helpful here

Thanks
   j

> I've increased PIXCLK up to 1ghz (as opposed to the default 500mhz) and this seem
> to hung the bridge.
>
>
> cheers,
> Petko
>
>
> On 22-08-15 16:52:59, Petko Manolov wrote:
> > 	Hello guys,
> >
> > I'm developing a driver for Sony imx492 sensor and i'm using imx8m-mini
> > (Variscite SoM on Symphony carrier board) platform.  Thanks to Laurent i dumped
> > the vendor mipi-csi and csi-bridge drivers in favor of mainline (v5.19-rc6 atm)
> > and parts started to click in place.  However, there are still a few rough
> > edges.
> >
> > The sensor is 47mpix, and is only capable of streaming over all four CSI-2
> > lanes.  Each lane is 1.728gbit, which makes 6.912gbps total bandwidth.
> > imx8m-mini's d-phy can handle (on paper) up to 6gbps.
> >
> > I guess the main question here is: what's the fastest transfer rate that's known
> > to work with this SoC?  Does anyone have experience with imx8m-mini in this
> > regard?
> >
> >
> > Even with the settings that i'm able to obtain a (distorted) test pattern image
> > with, i keep getting tons of:
> >
> > [99910.847591] imx-mipi-csis 32e30000.mipi-csi: FIFO Overflow Error events: 1353347
> >
> > IRQs also look a suspicious on the 'csi' part:
> >
> > 214:    2653716          0          0          0     GICv3  49 Level     32e30000.mipi-csi
> > 215:          2          0          0          0     GICv3  48 Level     csi
> >
> > That's with this clock setup:
> >
> >  sys_pll2                             1        1        0  1000000000          0     0  50000         Y
> >     sys_pll2_out                      5        5        0  1000000000          0     0  50000         Y
> >        sys_pll2_1000m                 3        3        0  1000000000          0     0  50000         Y
> >           csi1_phy_ref                1        1        0  1000000000          0     0  50000         Y
> >           csi1_core                   1        1        0   500000000          0     0  50000         Y
> >              csi1_root_clk            1        1        0   500000000          0     0  50000         Y
> >
> > However, if i change the latter two (csi1_core & csi1_root_clk) to 1ghz, there
> > are still mipi-csi IRQs coming in, but nothing from the csi-bridge.
> >
> > Any advice on where i shall start looking first?
> >
> >
> > thanks,
> > Petko

Re: Re: imx8m-mini csi-2 limitations

[Alexander Stein]

Hi Petko,

Am Donnerstag, 18. August 2022, 12:51:31 CEST schrieb Jacopo Mondi:
> Hi Petko
> 
> On Thu, Aug 18, 2022 at 12:27:45PM +0300, Petko Manolov wrote:
> > 	Hello again,
> > 
> > After digging down NXP's documentation and reading some comments within
> > kernel drivers (sorry Jacopo, you've left some nice comments in
> > imx7-media-csi.c, hence you're spammed now :) i came to the conclusion
> > that mipi-csi to csi-bridge data
> No worries.
> 
> I tried re-reading all the discussions, but memory still fails me
> here.
> 
> I recall I had an issue with the CSIS bandwidth and somewhere I
> suggested that it might be due to the CSI-2 specification version that
> the peripheral implemented. I can't find that email anymore though :/
> 
> > path can only be 8bits in raw12 format.  The only exception is YUV422
> > format, which get BIT_MIPI_DOUBLE_CMPNT flag set.
> 
> Yes, there has been quite some discussions about how to mix-and-match
> the settings between the CSIS (mipi-csi) and the CSI (csi-bridge) [*]
> 
> If I recall correctly there are at least three configurations at play:
> 
> - The CSIS pixel mode selection
> 
>   MIPI_CSI_ISP_CONFIG[13:12]
> 
>   The driver currently forces dual pixel sampling mode for YUV422
>   and report a TODO:
> 
>   * TODO: Verify which other formats require DUAL (or QUAD) modes.
> 
>   Here you're trying to transfer RAW12 data, which is indicated in the
>   register documentation as one of the formats suitable for DUAL/QUAD
>   mode transfer
> 
>   - I'm actually not sure how and if RAW12 gets expanded to 16 bit
>     samples by filling the 16-bit word with 0s or it either gets
>     packed in 6 bytes with no paddings. Figure "13-33. Pixel
>     alignment" seems to suggest that, but I'm not sure I really got
>     that diagram
> 
> - The CSI-bridge
> 
>   - CSI_CR3[3] SENSOR_16BITS
>   - CSI_CR18[20] MIPI_DOUBLE_CMP
> 
>   The comment in imx7_csi_configure() explains how different versions
>   of YUYV (2X8 and 1X16) are handled, and why SENSOR_16BITS and
>   MIPI_DOUBLE_CMP have to be enabled when the csi-bridge has to be
> instructed to sample 16 bits samples from the RX queue.
> 
> I guess the key would be here to find out what combination of
> SINGLE/DUAL/QUAD sampling is opportune for RAW12 (I would try with
> DUAL first and then QUAD) and then configure the csi-bridge bus
> sampling mode accordingly (likely in the same was as it is done for
> YUYV_1X16)
> 
> When it comes to bandwidth limitation, can you try to reduce the
> sensor output size to make sure you chase one issue at the time ?
> 
> [*] Is "CSI" the most abused acronym of history ?
> 
> > So i guess there are two questions:
> > 	a) can the csi-bridge (and mipi-csi) be persuaded to do two-bytes 
for
> > 	raw12 format;
> 
> See above :)
> 
> > 	b) what's the maximum frequency for csi-bridge PIXCLK?

While it does not exactly answer your question, the i.MX8M Mini Datasheet 
(both for Commercial and Industrial) mentions "four-lane MIPI camera serial 
interfaces, which operates up to a maximum bit rate of 1.5 Gbps".
I would assume the bridge is capable of handling the full link speed on four 
lanes, otherwise this would be quite useless.

Best regards,
Alexander

Re: Re: imx8m-mini csi-2 limitations

[Petko Manolov]

On 22-08-18 14:41:18, Alexander Stein wrote:
> Hi Petko,

Hi Alexander,

<snip>

> While it does not exactly answer your question, the i.MX8M Mini Datasheet 
> (both for Commercial and Industrial) mentions "four-lane MIPI camera serial 
> interfaces, which operates up to a maximum bit rate of 1.5 Gbps". I would 
> assume the bridge is capable of handling the full link speed on four lanes, 
> otherwise this would be quite useless.

Ahem, if that the case (useless), it won't be a first.

In theory the d-phy should support 2.5gbps, but in practice it is only 1.5gbps.  
If CSIS to CSI (bridge) can't be made to transfer 16bit words for 12 bit raw 
format and if the frequency between both can go up to 500mhz, this leaves us 
with 4gbps (8bit x 500mhz) max bandwidth.

If the above calculation is correct, this leaves us with only one option - limit 
the speed of the camera sensor.


cheers,
Petko

Re: imx8m-mini csi-2 limitations

[Petko Manolov]

On 22-08-18 12:51:31, Jacopo Mondi wrote:
> Hi Petko
> 
> On Thu, Aug 18, 2022 at 12:27:45PM +0300, Petko Manolov wrote:
> > 	Hello again,
> >
> > After digging down NXP's documentation and reading some comments within 
> > kernel drivers (sorry Jacopo, you've left some nice comments in 
> > imx7-media-csi.c, hence you're spammed now :) i came to the conclusion that 
> > mipi-csi to csi-bridge data
> 
> No worries.
> 
> I tried re-reading all the discussions, but memory still fails me here.
> 
> I recall I had an issue with the CSIS bandwidth and somewhere I suggested that 
> it might be due to the CSI-2 specification version that the peripheral 
> implemented. I can't find that email anymore though :/

Well, only bumping up the frequency (to 1ghz) between the CSIS and bridge does 
not work out of the box.  The latter stopped generating IRQs, which kind of 
ruined the day for me.  It would be better if i know if that's at all possible, 
before start debugging the issue.

> Yes, there has been quite some discussions about how to mix-and-match the 
> settings between the CSIS (mipi-csi) and the CSI (csi-bridge) [*]
> 
> If I recall correctly there are at least three configurations at play:
> 
> - The CSIS pixel mode selection
> 
>   MIPI_CSI_ISP_CONFIG[13:12]

Got this one.

>   The driver currently forces dual pixel sampling mode for YUV422 and report a 
>   TODO:
> 
>   * TODO: Verify which other formats require DUAL (or QUAD) modes.
> 
>   Here you're trying to transfer RAW12 data, which is indicated in the 
>   register documentation as one of the formats suitable for DUAL/QUAD mode 
>   transfer
> 
>   - I'm actually not sure how and if RAW12 gets expanded to 16 bit samples by 
>     filling the 16-bit word with 0s or it either gets packed in 6 bytes with 
>     no paddings. Figure "13-33. Pixel alignment" seems to suggest that, but 
>     I'm not sure I really got that diagram
> 
> - The CSI-bridge
> 
>   - CSI_CR3[3] SENSOR_16BITS
>   - CSI_CR18[20] MIPI_DOUBLE_CMP

Ah, i did not set CSI_CR3 when i (quickly) tried to go to 16bit data width.  
I'll give it another try based on the above.

>   The comment in imx7_csi_configure() explains how different versions of YUYV 
>   (2X8 and 1X16) are handled, and why SENSOR_16BITS and MIPI_DOUBLE_CMP have 
>   to be enabled when the csi-bridge has to be instructed to sample 16 bits 
>   samples from the RX queue.

OK.

> I guess the key would be here to find out what combination of SINGLE/DUAL/QUAD 
> sampling is opportune for RAW12 (I would try with DUAL first and then QUAD) 
> and then configure the csi-bridge bus sampling mode accordingly (likely in the 
> same was as it is done for YUYV_1X16)

I've come across this comment in imx-mipi-csis.c left by you earlier this year:

"Neither of the IP cores connected to the CSIS in i.MX SoCs (CSI bridge or ISI) 
support quad pixel mode, so this will never work in practice."

I guess, if true, it doesn't make sense to waste time on quad mode.

> When it comes to bandwidth limitation, can you try to reduce the sensor output 
> size to make sure you chase one issue at the time ?

I am at Sony's mercy here.  The datasheed it full of holes and i get feeded 
small bits of information at irregular intervals.  I asked them to provide me 
with register setup for much slower data rate & pixel clock (at full speed the 
damn thing is streaming at almost 7gbps), but i'm still waiting...

> [*] Is "CSI" the most abused acronym of history ?

Maybe.  I already hate spelling this acronym even in my mind. :)

> > So i guess there are two questions:
> >
> > 	a) can the csi-bridge (and mipi-csi) be persuaded to do two-bytes for
> > 	raw12 format;
> 
> See above :)
> 
> > 	b) what's the maximum frequency for csi-bridge PIXCLK?
> >
> 
> Not sure about this one.
> 
> I've anyway cc-ed Laurent and Xavier, which can surely be helpful here

Thanks a bunch, the above information is very helpful.


cheers,
Petko

Re: imx8m-mini csi-2 limitations

[Laurent Pinchart]

Hello,

On Thu, Aug 18, 2022 at 06:37:23PM +0300, Petko Manolov wrote:
> On 22-08-18 12:51:31, Jacopo Mondi wrote:
> > On Thu, Aug 18, 2022 at 12:27:45PM +0300, Petko Manolov wrote:
> > > 	Hello again,
> > >
> > > After digging down NXP's documentation and reading some comments within 

Please note that the documentation is sometimes confusing and sometimes
incorrect (it would be too easy otherwise, wouldn't it ?).

How to configure the CSIS output bus depends on the SoC integration. If
I recall correctly, all i.MX SoCs that connect the CSIS to a CSI bridge
have the same integration, but when the CSIS is connected to other IP
cores, configuration requirements may vary.

> > > kernel drivers (sorry Jacopo, you've left some nice comments in 
> > > imx7-media-csi.c, hence you're spammed now :) i came to the conclusion that 
> > > mipi-csi to csi-bridge data
> > 
> > No worries.
> > 
> > I tried re-reading all the discussions, but memory still fails me here.
> > 
> > I recall I had an issue with the CSIS bandwidth and somewhere I suggested that 
> > it might be due to the CSI-2 specification version that the peripheral 
> > implemented. I can't find that email anymore though :/
> 
> Well, only bumping up the frequency (to 1ghz) between the CSIS and bridge does 
> not work out of the box.  The latter stopped generating IRQs, which kind of 
> ruined the day for me.  It would be better if i know if that's at all possible, 
> before start debugging the issue.
> 
> > Yes, there has been quite some discussions about how to mix-and-match the 
> > settings between the CSIS (mipi-csi) and the CSI (csi-bridge) [*]
> > 
> > If I recall correctly there are at least three configurations at play:
> > 
> > - The CSIS pixel mode selection
> > 
> >   MIPI_CSI_ISP_CONFIG[13:12]
> 
> Got this one.
> 
> >   The driver currently forces dual pixel sampling mode for YUV422 and report a 
> >   TODO:
> > 
> >   * TODO: Verify which other formats require DUAL (or QUAD) modes.
> > 
> >   Here you're trying to transfer RAW12 data, which is indicated in the 
> >   register documentation as one of the formats suitable for DUAL/QUAD mode 
> >   transfer
> > 
> >   - I'm actually not sure how and if RAW12 gets expanded to 16 bit samples by 
> >     filling the 16-bit word with 0s or it either gets packed in 6 bytes with 
> >     no paddings. Figure "13-33. Pixel alignment" seems to suggest that, but 
> >     I'm not sure I really got that diagram

That would imply a 48-bit bus between the CSIS and the CSI bridge, and I
don't think that's the case.

When reading the CSIS documentation, keep in mind that the IP comes from
a third party (Samsung). The CSIS documentation in the i.MX8MM reference
manual comes from a generic documentation of the IP core, which offers
different output bus widths (among other integration options). It
doesn't precisely describe the synthesis options uses in the i.MX8MM.

> > - The CSI-bridge
> > 
> >   - CSI_CR3[3] SENSOR_16BITS
> >   - CSI_CR18[20] MIPI_DOUBLE_CMP
> 
> Ah, i did not set CSI_CR3 when i (quickly) tried to go to 16bit data width.  
> I'll give it another try based on the above.
> 
> >   The comment in imx7_csi_configure() explains how different versions of YUYV 
> >   (2X8 and 1X16) are handled, and why SENSOR_16BITS and MIPI_DOUBLE_CMP have 
> >   to be enabled when the csi-bridge has to be instructed to sample 16 bits 
> >   samples from the RX queue.
> 
> OK.
> 
> > I guess the key would be here to find out what combination of SINGLE/DUAL/QUAD 
> > sampling is opportune for RAW12 (I would try with DUAL first and then QUAD) 
> > and then configure the csi-bridge bus sampling mode accordingly (likely in the 
> > same was as it is done for YUYV_1X16)
> 
> I've come across this comment in imx-mipi-csis.c left by you earlier this year:
> 
> "Neither of the IP cores connected to the CSIS in i.MX SoCs (CSI bridge or ISI) 
> support quad pixel mode, so this will never work in practice."
> 
> I guess, if true, it doesn't make sense to waste time on quad mode.

To the best of my recollection, that's accurate.

> > When it comes to bandwidth limitation, can you try to reduce the sensor output 
> > size to make sure you chase one issue at the time ?
> 
> I am at Sony's mercy here.  The datasheed it full of holes and i get feeded 
> small bits of information at irregular intervals.  I asked them to provide me 
> with register setup for much slower data rate & pixel clock (at full speed the 
> damn thing is streaming at almost 7gbps), but i'm still waiting...
> 
> > [*] Is "CSI" the most abused acronym of history ?
> 
> Maybe.  I already hate spelling this acronym even in my mind. :)
> 
> > > So i guess there are two questions:
> > >
> > > 	a) can the csi-bridge (and mipi-csi) be persuaded to do two-bytes for
> > > 	raw12 format;
> > 
> > See above :)
> > 
> > > 	b) what's the maximum frequency for csi-bridge PIXCLK?
> > >
> > 
> > Not sure about this one.
> > 
> > I've anyway cc-ed Laurent and Xavier, which can surely be helpful here
> 
> Thanks a bunch, the above information is very helpful.

-- 
Regards,

Laurent Pinchart

Re: imx8m-mini csi-2 limitations

[Petko Manolov]

On 22-08-18 12:51:31, Jacopo Mondi wrote:
>

<snip>

> If I recall correctly there are at least three configurations at play:
> 
> - The CSIS pixel mode selection
> 
>   MIPI_CSI_ISP_CONFIG[13:12]

Funny enough adding MIPI_CSIS_ISPCFG_PIXEL_MODE_QUAD and 
MIPI_CSIS_ISPCFG_ALIGN_32BIT to the config(0) register actually produced an 
image.  Highly distorted image, but did not break the image acquisition.

MIPI_CSIS_ISPCFG_ALIGN_32BIT seems to be the wrong flag here, but it without it 
the streaming got blocked.

>   The driver currently forces dual pixel sampling mode for YUV422
>   and report a TODO:
> 
>   * TODO: Verify which other formats require DUAL (or QUAD) modes.
> 
>   Here you're trying to transfer RAW12 data, which is indicated in the
>   register documentation as one of the formats suitable for DUAL/QUAD
>   mode transfer
> 
>   - I'm actually not sure how and if RAW12 gets expanded to 16 bit
>     samples by filling the 16-bit word with 0s or it either gets
>     packed in 6 bytes with no paddings. Figure "13-33. Pixel
>     alignment" seems to suggest that, but I'm not sure I really got
>     that diagram
> 
> - The CSI-bridge
> 
>   - CSI_CR3[3] SENSOR_16BITS

Actually the driver is always setting this one for raw10/12 formats.

>   - CSI_CR18[20] MIPI_DOUBLE_CMP

Enabling this bit for raw10/12 formats kills the transmission.  According to the 
documentation this flag transfers full pixel per clock cycle as opposed to just 
half a pixel.

>   The comment in imx7_csi_configure() explains how different versions of YUYV 
>   (2X8 and 1X16) are handled, and why SENSOR_16BITS and MIPI_DOUBLE_CMP have 
>   to be enabled when the csi-bridge has to be instructed to sample 16 bits 
>   samples from the RX queue.

Seems like i have to find a way to make the mipi-csi stream full pixel (iow 
16bit), if any such thing exists.  And hope this configuration is supported 
between both parts, mipi & bridge.

> I guess the key would be here to find out what combination of SINGLE/DUAL/QUAD 
> sampling is opportune for RAW12 (I would try with DUAL first and then QUAD) 
> and then configure the csi-bridge bus sampling mode accordingly (likely in the 
> same was as it is done for YUYV_1X16)

In fact i was mimicking MEDIA_BUS_FMT_YUYV8_1X16 case, but as mentioned, this 
didn't work.  Seems like raw10/12 formats are not so well (if at all) handled by 
the bridge.

> When it comes to bandwidth limitation, can you try to reduce the sensor output 
> size to make sure you chase one issue at the time ?

I used insanely big vblank and hblank values.  Obtaining single frame took about 
90 seconds.  This indeed reduced "FIFO Overflow Error" and "Frame Size Error" to 
four digit number (the lowest rate i've seen so far), but there was no visible 
improvement in the captured test pattern image.

I doubt i can make the sensor stream slower and i also think it doesn't make 
sense to go down this path - there are still errors.

Any advice on how to debug the CSI bridge?  NXP support is as useless as ever.


cheers,
Petko