Re: [PATCH v2] media: ov5640: add support of V4L2_CID_LINK_FREQ

[Hugues FRUCHET <hugues.fruchet@st.com>]

Hi Jacopo, all,

Back on this subject recently, I've found interesting things around 
register 0x4837 PCLK PERIOD thanks to Samuel Bobrowicz work on PLL 
settings [1], but 0x4837 register value computation differs from what 
I've understood/measured.

The OV5640 PCLK_PERIOD register value must be in line with the
ST MIPID02 CSI-2 receiver CLOCK_LANE_1 register, otherwise receptions 
issues are encountered has shown in my previous mail.

Configuring those 2 registers according to measured MIPI clock frequency
allows to cover almost all resolutions/formats (RGB565, YUV422, JPEG).
I've also measured with oscilloscope the MIPI clock-lane frequency and 
verified that this is well matching computed one [2].
Please note that due to platform limitation, I could not test link 
frequency above 720p@15fps, so additional tests are needed with platform 
that could handle 5Mp@15fps (OV5640 limit).

In term of code, this mean:

v4l2_ctrl_new_int_menu(hdl, ops, V4L2_CID_LINK_FREQ,
        		  0, 0, link_freq_menu_items);

ov5640_set_mipi_pclk(rate)
{
   mipi_sclk = ov5640_calc_sys_clk(sensor, rate, &prediv, &mult, &sysdiv);
   link_freq = mipi_sclk / 2 / mipi_div; /* the CSI-2 clock-lane 
frequency, measurements are matching */

   _pclk_period = (u8) (2000000000UL / link_freq);/* expressed in ns and 
with 1-bit decimal: 0x1=0.5ns, 0x2=1ns, 0x3=1.5ns and so on... */
   ov5640_write_reg(sensor, OV5640_REG_PCLK_PERIOD, _pclk_period);

   link_freq_menu_items[0] = link_freq;/* Currently a hack to inform 
receiver about the dynamically computed clock frequency, I don't know 
yet how to handle this correctly, please advise... */

   ...
}

As explained in comment, I miss a V4L2 way to set dynamically 
V4L2_CID_LINK_FREQ in order to propose a new patchset.


[1] 
https://patchwork.kernel.org/project/linux-media/patch/1539797508-127629-1-git-send-email-sam@elite-embedded.com/

[2] measure of the CSI-2 clock frequency, tested with JPEG (easier to 
check that capture is fine) and various resolutions:

****************
***  QQVGA  ****
****************
* JPEG QQVGA@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=160,height=120,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[  371.459607] ov5640 1-003c: Bandwidth Per Lane=223879680, 160x120 from 
1896x984
[  371.465516] ov5640 1-003c: mipi_sclk=224000000, mipi_div=2, prediv=3, 
mult=28, sysdiv=1
[  371.473727] ov5640 1-003c: link freq=56000000 Hz
[  371.478529] ov5640 1-003c: PCLK PERIOD 0x4837=0x23
[  371.538193] st-mipid02 2-0014: clk_lane_reg1=0x8d
<<<<<<<<<<<<<<<<< 15.09 fps
<<<<<<<<<<<<<<< 15.04 fps
<<<<<<<<<<<<<<< 15.03 fps
<<<<<<<<<<<<<<< 15.02 fps
<<<<<<<<<<<<<<< 15.01 fps
Clock-lane frequency measured at #18ns (55.5MHz)


* RGB565 QQVGA@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=160,height=120,pixelformat=RGBP --stream-mmap 
--stream-count=-1
[ 1229.422079] st-mipid02 2-0014: clk_lane_reg1=0x8d
[ 1229.431758] ov5640 1-003c: Bandwidth Per Lane=223879680, 160x120 from 
1896x984
[ 1229.437905] ov5640 1-003c: mipi_sclk=224000000, mipi_div=2, prediv=3, 
mult=28, sysdiv=1
[ 1229.445620] ov5640 1-003c: link freq=56000000 Hz
[ 1229.450397] ov5640 1-003c: PCLK PERIOD 0x4837=0x23
<<<<<<<<<<<<<<<<< 15.09 fps
<<<<<<<<<<<<<<< 15.04 fps
<<<<<<<<<<<<<< 14.70 fps
<<<<<<<<<<<<<<< 14.77 fps
Measured #18ns (55.5MHz)


**************
***  VGA  ****
**************
* JPEG VGA@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=640,height=480,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[ 1105.621884] ov5640 1-003c: Bandwidth Per Lane=245721600, 640x480 from 
1896x1080
[ 1105.627927] ov5640 1-003c: mipi_sclk=246000000, mipi_div=2, prediv=3, 
mult=123, sysdiv=4
[ 1105.641273] ov5640 1-003c: link freq=61500000 Hz
[ 1105.646789] ov5640 1-003c: PCLK PERIOD 0x4837=0x40
[ 1105.709626] st-mipid02 2-0014: clk_lane_reg1=0x81
<<<<<<<<<<<<<<<<< 15.09 fps
<<<<<<<<<<<<<<< 15.04 fps
<<<<<<<<<<<<<<< 15.03 fps
<<<<<<<<<<<<<<< 15.02 fps
<<<<<<<<<<<<<<< 15.01 fps

Measured #16ns (62.5MHz)


* JPEG VGA@30fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=30;v4l2-ctl 
--set-fmt-video=width=640,height=480,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[ 1144.539082] ov5640 1-003c: Bandwidth Per Lane=491443200, 640x480 from 
1896x1080
[ 1144.545143] ov5640 1-003c: mipi_sclk=492000000, mipi_div=2, prediv=3, 
mult=123, sysdiv=2
[ 1144.558756] ov5640 1-003c: link freq=123000000 Hz
[ 1144.562012] ov5640 1-003c: PCLK PERIOD 0x4837=0x20
[ 1144.623895] st-mipid02 2-0014: clk_lane_reg1=0x41
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.09 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.04 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.13 fps

Measured #8ns (125MHz)


*******************
***  1024x768  ****
*******************
* JPEG 1024x768@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=1024,height=768,pixelformat=JPEG --stream-mmap 
--stream-count=-1
<<<<<<<<<<<<<<<<< 15.09 fps
<<<<<<<<<<<<<<< 15.04 fps
<<<<<<<<<<<<<<< 15.03 fps
<<<<<<<<<<<<<<< 15.02 fps

Measured #16ns (62.5MHz)


* JPEG 1024x768@30fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=30;v4l2-ctl 
--set-fmt-video=width=1024,height=768,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[ 1218.632061] ov5640 1-003c: Bandwidth Per Lane=491443200, 1024x768 
from 1896x1080
[ 1218.638216] ov5640 1-003c: mipi_sclk=492000000, mipi_div=2, prediv=3, 
mult=123, sysdiv=2
[ 1218.651788] ov5640 1-003c: link freq=123000000 Hz
[ 1218.655345] ov5640 1-003c: PCLK PERIOD 0x4837=0x20
[ 1218.724149] st-mipid02 2-0014: clk_lane_reg1=0x41
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.09 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.04 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.13 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.09 fps
Measured #8ns (125MHz)


***************
***  720p  ****
***************
* JPEG 720p@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=1280,height=720,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[ 7781.232498] ov5640 1-003c: Bandwidth Per Lane=168009600, 1280x720 
from 1892x740
[ 7781.238554] ov5640 1-003c: mipi_sclk=169600000, mipi_div=1, prediv=3, 
mult=106, sysdiv=5
[ 7781.247117] ov5640 1-003c: link freq=84800000 Hz
[ 7781.251116] ov5640 1-003c: PCLK PERIOD 0x4837=0x17
[ 7781.316980] st-mipid02 2-0014: clk_lane_reg1=0x5d

Measured #12ns (83MHz)

* JPEG 720p@30fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=30;v4l2-ctl 
--set-fmt-video=width=1280,height=720,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[  515.548519] ov5640 1-003c: Bandwidth Per Lane=336019200, 1280x720 
from 1892x740
[  515.554646] ov5640 1-003c: mipi_sclk=340000000, mipi_div=1, prediv=3, 
mult=85, sysdiv=2
[  515.562406] ov5640 1-003c: link freq=170000000 Hz
[  515.574376] ov5640 1-003c: PCLK PERIOD 0x4837=0xb
[  515.639862] st-mipid02 2-0014: clk_lane_reg1=0x2d
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.39 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.50 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.36 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.42 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.40 fps
Measured #6ns (166MHz)
==> 30fps but image artefacts (out of MP1 capabilities)


****************
***  1080p  ****
****************
* JPEG HD@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=1920,height=1080,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[ 1998.266915] ov5640 1-003c: Bandwidth Per Lane=336000000, 1920x1080 
from 2500x1120
[ 1998.273040] ov5640 1-003c: mipi_sclk=336000000, mipi_div=1, prediv=3, 
mult=42, sysdiv=1
[ 1998.280987] ov5640 1-003c: link freq=168000000 Hz
[ 1998.286142] ov5640 1-003c: PCLK PERIOD 0x4837=0xb
[ 1998.380206] st-mipid02 2-0014: clk_lane_reg1=0x2d
<<< 1.88 fps
<< 1.87 fps
<< 1.88 fps
<< 1.87 fps
<< 1.87 fps
Measured #6ns (166MHz)

* JPEG HD@30fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=30;v4l2-ctl 
--set-fmt-video=width=1920,height=1080,pixelformat=JPEG --stream-mmap 
--stream-count=-1
[ 2196.981767] ov5640 1-003c: Bandwidth Per Lane=672000000, 1920x1080 
from 2500x1120
[ 2196.987882] ov5640 1-003c: mipi_sclk=672000000, mipi_div=1, prediv=3, 
mult=84, sysdiv=1
[ 2196.996225] ov5640 1-003c: link freq=336000000 Hz
[ 2197.000553] ov5640 1-003c: PCLK PERIOD 0x4837=0x5
[ 2197.097244] st-mipid02 2-0014: clk_lane_reg1=0x15
Measured #3ns (333MHz)

==> no images but out of MP1 capabilities


**************
***  5Mp  ****
**************
* JPEG 5Mp@15fps
v4l2-ctl --set-ctrl=test_pattern=1;v4l2-ctl --set-parm=15;v4l2-ctl 
--set-fmt-video=width=2592,height=1944,pixelformat=JPEG --stream-mmap 
--stream-count=-1

[ 2479.203457] ov5640 1-003c: Bandwidth Per Lane=671639040, 2592x1944 
from 2844x1968
[ 2479.209647] ov5640 1-003c: mipi_sclk=672000000, mipi_div=1, prediv=3, 
mult=84, sysdiv=1
[ 2479.217961] ov5640 1-003c: link freq=336000000 Hz
[ 2479.222240] ov5640 1-003c: PCLK PERIOD 0x4837=0x5
[ 2479.388400] st-mipid02 2-0014: clk_lane_reg1=0x15

Measured #3ns (333MHz)

==> no images but out of MP1 capabilities



On 9/3/19 4:48 PM, Hugues FRUCHET wrote:
> Hi Jacopo,
> 
> On 8/21/19 4:24 PM, Jacopo Mondi wrote:
>> Hello,
>>      +laura who has been working on supporting RAW capture for this
>>      driver.
>>
>> On Tue, Aug 20, 2019 at 12:13:12PM +0300, Sakari Ailus wrote:
>>> Hi Hugues,
>>>
>>> On Tue, Jul 02, 2019 at 04:05:46PM +0000, Hugues FRUCHET wrote:
>>>> Hi Sakari,
>>>>
>>>> On 6/27/19 6:05 PM, Sakari Ailus wrote:
>>>>> Hi Hugues,
>>>>>
>>>>> On Thu, Jun 27, 2019 at 02:57:04PM +0200, Hugues Fruchet wrote:
>>>>>> Add support of V4L2_CID_LINK_FREQ, this is needed
>>>>>> by some CSI-2 receivers.
>>>>>>
>>>>>> 384MHz is exposed for the time being, corresponding
>>>>>> to 96MHz pixel clock with 2 bytes per pixel on 2 data lanes.
>>>>>>
>>>>>> This setup has been tested successfully with ST MIPID02
>>>>>> CSI-2 to parallel bridge.
>>>>>>
>>>>>> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
>>>>>> ---
>>>>>
>>>>> Thanks for the patch.
>>>>>
>>>>> The driver calculates the sensor configuration based on its configuration,
>>>>> and this needs to be reflected in the link frequency: it's not a static
>>>>> value. See e.g. ov5640_calc_sys_clk().
>>>>>
>>>>
>>>> I know this code, but for a reason I don't understand yet, this seems
>>>> to not have effects on the CSI-2 link frequency.
>>>>
>>
>> This seems unlikely to me, as the ov5640_calc_sys_clk() calculates the
>> system clock, which then generates the MIPI CLK.
>>
>> I would really be interested to know if you could measure somehow the
>> actual frequency of the clock lane, to make sure it actually
>> changes according to to the driver calculations.
>>
>>>> This has been verified with MIPID02 CSI-2 bridge which only work with
>>>> this fixed link frequency as input to program its ui_x4 register
>>>> setting, see
>>>> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2028171.html.
>>>> All resolutions and all framerate have been tested succesfully with this
>>>> setting.
>>>>
>>>> Initially I tried to set the link frequency according to the value
>>>> computed in ov5640_calc_sys_clk() but it was only functional when
>>>> resolutions/framerate was close to the 384MHz value...
>>>>
>>>> As OV5640 D3 engineering board has been initially developped for
>>>> dragonboard, I'll dig into this and found this commit:
>>>> https://lore.kernel.org/patchwork/patch/886794/
>>>> which set a fixed pixel rate value to 96MHz, which match perfectly
>>>> with the 384MHz value I found for link frequency...
>>>>
>>>> Perhaps other CSI-2 OV5640 users can comment about it and have the
>>>> explanations of what I experiment...
>>>> Maxime, Jacopo, do you have any idea about it ?
>>>
>>> I would also like to wee a comment from someone who's familiar with the
>>> device. Yet I can tell a static value of 348 MHz is clearly incorrect as it
>>> ignores sensor runtime configuration as well as platform configuration
>>> (external clock frequency for instance).
>>>
>>> Generally speaking, configuring a CSI-2 receiver to expect a particular
>>> frequency usually doesn't mean it's going to fail even if the transmitter
>>> uses a different frequency, albeit the likelihood of it not working
>>> increases as the difference grows. Could the problem be at the receiver's
>>> end?
>>>
>>> Have you checked what kind of values ov5640_calc_pclk() returns for
>>> different configurations? It would seem like that this is what the
>>> LINK_FREQ (divided by lanes and multiplied by two) should be.
>>
>> Not exactly. ov5640_calc_pclk() is only used when computing the
>> parallel bus pixel clock not for the CSI-2 bus.
>>
>> To obtain the link frequency for the MIPI interface I would consider
>> the system clock frequency calculated by ov5640_calc_sys_clk(), which
>> represents the bandwidth per lane in bits per second. This should then
>> be divided by 2 to compensate the MIPI DDR mode [*] (no need to divide
>> by the number of lanes, as this is already the bandwidth -per lane-)
>>
>> For 640x480 YUYV8_2X8 (and 1024x768) with 2 data lanes and 24MHz xclk
>> I have calculated the following values:
>>
>> SYSCLK = 492MHz
>> MIPISCLK = 256MHz
>> PCLK = 61,50MHz
>>
>> For 1280x720 with the same setup
>> SYSCLK = 340MHz
>> MIPI_CLK = 170MHz
>> PCLK = 42,50 (this seems veeery low according to datasheet)
>>
>> For 1920x1080
>> SYSCLK = 680MHz
>> MIPI_CLK = 340MHz
>> PCLK = 85MHz (slightly slow according to the datasheet)
>>
>> All captured images seems fine...
>>
>> If you could confirm those values by probing the actual clock lane it
>> would be just great.
>>
> 
> I've made some measurements probing clock lane with YUYV 16 bits
> grabbing, here are the results:
> 
> * VGA @ 30fps
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=640,height=480,pixelformat=YUYV --stream-mmap
> [ 1624.854273] ov5640 0-003c: rate=491443200, 640x480 from 1896x1080
> [ 1624.859192] ov5640 0-003c: sysclk=492000000, mipi_div=2
> Measured clock lane frequency: 123MHz
> 
> * 1024x768 @ 30fps
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=1024,height=768,pixelformat=YUYV --stream-mmap
> [  558.833885] ov5640 0-003c: rate=491443200, 1024x768 from 1896x1080
> [  558.840188] ov5640 0-003c: sysclk=492000000, mipi_div=2
> Measured clock lane frequency: 124MHz
> 
> * 720p @ 30fps
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=1280,height=720,pixelformat=YUYV --stream-mmap
> [ 2920.785392] ov5640 0-003c: rate=336019200, 1280x720 from 1892x740
> [ 2920.794771] ov5640 0-003c: sysclk=340000000, mipi_div=1
> Measured clock lane frequency: 171MHz
> 
> * 1080p @ 30fps
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=1920,height=1080,pixelformat=YUYV --stream-mmap
> [ 1650.143701] ov5640 0-003c: rate=672000000, 1920x1080 from 2500x1120
> [ 1650.149876] ov5640 0-003c: sysclk=672000000, mipi_div=1
> Measured clock lane frequency: 330MHz
> 
> So it seems that formula must also take care of mipi_div:
> link_frequency = sys_div / 2 / mipi_div
> 
> 
> Unfortunately, as said previously, when updating ov5640 codebase so that
> CID_LINK_FREQUENCY returns this computed value instead of 384MHz fixed
> value, the MIPID02 bridge has some troubles and some
> resolutions/framerate are broken:
> 
> dmesg -n8
> echo "format link_freq +p" > /sys/kernel/debug/dynamic_debug/control
> 
> * VGA @ 30fps => broken
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=640,height=480,pixelformat=YUYV --stream-mmap
> [ 1624.854273] ov5640 0-003c: rate=491443200, 640x480 from 1896x1080
> [ 1624.859192] ov5640 0-003c: sysclk=492000000, mipi_div=2
> [ 1624.924287] st-mipid02 1-0014: detect link_freq = 123000000 Hz
> ==> no frames sent to DCMI
> 
> * 720p @ 30fps => very slow framerate
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=1280,height=720,pixelformat=YUYV --stream-mmap
> [ 1900.707822] ov5640 0-003c: rate=336019200, 1280x720 from 1892x740
> [ 1900.712717] ov5640 0-003c: sysclk=340000000, mipi_div=1
> [ 1900.782402] st-mipid02 1-0014: detect link_freq = 170000000 Hz
> << 0.69 fps
> < 0.67 fps
> < 0.67 fps
> 
> * 1080p @ 30fps => very slow framerate
> v4l2-ctl --set-parm=30;v4l2-ctl
> --set-fmt-video=width=1920,height=1080,pixelformat=YUYV --stream-mmap
> [ 1366.550832] ov5640 0-003c: rate=336000000, 1920x1080 from 2500x1120
> [ 1366.555668] ov5640 0-003c: sysclk=336000000, mipi_div=1
> Frame rate set to 30.000 fps
> [ 1367.105503] ov5640 0-003c: rate=672000000, 1920x1080 from 2500x1120
> [ 1367.110420] ov5640 0-003c: sysclk=672000000, mipi_div=1
> [ 1367.214498] st-mipid02 1-0014: detect link_freq = 336000000 Hz
> << 0.11 fps
> < 0.11 fps
> 
> 
> * 1080p @ 15fps => OK, 15fps as expected
> v4l2-ctl --set-parm=15;v4l2-ctl
> --set-fmt-video=width=1920,height=1080,pixelformat=YUYV --stream-mmap
> [ 1327.417545] ov5640 0-003c: rate=336000000, 1920x1080 from 2500x1120
> [ 1327.422560] ov5640 0-003c: sysclk=336000000, mipi_div=1
> [ 1327.527852] st-mipid02 1-0014: detect link_freq = 168000000 Hz
> <<<<<<<<<<<<<<<<< 15.09 fps
> <<<<<<<<<<<<<<< 15.04 fps
> 
> 
> One could argue that this is the mipid02 bridge codebase that is wrong:
> drivers/media/i2c/st-mipid02.c:
>     mipid02_configure_from_rx_speed()
>       [...]
>       bridge->r.clk_lane_reg1 |= (2000000000 / link_freq) << 2;
> 
> but computation is inline with MIPID02 spec:
> 
> "CLOCK LANE 1 REGISTER"
> Bit_no   Bit_name
> 7        ui_x4_clk_lane[5]
> 6        ui_x4_clk_lane[4]
> 5        ui_x4_clk_lane[3]
> 4        ui_x4_clk_lane[2]
> 3        ui_x4_clk_lane[1]
> 2        ui_x4_clk_lane[0]
> Unit interval time multiplied by four
> This signal indicates the bit period in units of
> 0.25 ns. If the unit interval is 3 ns, twelve (0x0C)
> should be programmed. This value is used to
> generate delays. Therefore, if the period is not a
> multiple of 0.25 ns, the value should be rounded
> down. For example, a 600 Mbit/s single lane
> linkuses a unit interval of 1.667 ns. Multiplying
> by four results in 6.667. In this case, a value of 6
> (not 7) should be programmed.
> 
> 
> Perhaps that someone which knows well CSI-2 interfaces could
> detect what is wrong here, but personally I don't.
> 
> 
>> However, this only work assuming the here below [*], and we're still
>> missing something because RAW still doesn't work as expected :(
>>
>> Anyway, clock tree madness apart, fixing the LINK_FREQ control value
>> to 96MHz seems like it does not reflect what the driver actual does.
>>
>> Could you try setting the control value to what the driver actually
>> computes as here suggested?
>>
>> Thanks
>>      j
>>
>> PS. I'm still confused why the have the link-frequencies property in
>> DTS bindings. What is its purpose if all drivers compute or hardcode
>> it?
> 
> I share this point of view, I don't know how to return a dynamically
> computed link frequency. Current drivers are exposing a single one
> or a set of discrete frequencies.
> For a matter of test purpose, I've done this hack:
> 
> -static const s64 link_freq_menu_items[] = {
> +static s64 link_freq_menu_items[] = {
> 	384000000,
> };
> 
> +	link_freq_menu_items[0] = _rate / 2 / mipi_div;
> 
> 
>>
>> [*] There is a big assumption here, that the MIPI bus clock gets
>> generated by two different clock outputs depending if the mode goes
>> through the the scaler or not. You can see this at line 967 in the
>> driver code. If mode goes though the scaler, MIPI_DIV = 2 and you get
>> the bus clock from the MIPISCLK signal. If it does not go through the
>> scaler MIPI_DIV = 1 and then the MIPI bus clock gets provided by the
>> MIPI_CLK signal. This is the result of several attempts to decode the
>> ov5640 clock tree, but it has only been tested with modes with bpp =
>> 16 and 2 data lanes. As it has been recently reported, for RAW mode,
>> this does not work well, so the assumption might not be correct.
>>
>>>
>>>>
>>>>
>>>>>> version 2:
>>>>>>      - do not set control read only as per Hans' comment:
>>>>>>        See https://www.mail-archive.com/linux-media@vger.kernel.org/msg147910.html
>>>>>>
>>>>>>     drivers/media/i2c/ov5640.c | 10 ++++++++++
>>>>>>     1 file changed, 10 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c
>>>>>> index 82d4ce9..e6307f3 100644
>>>>>> --- a/drivers/media/i2c/ov5640.c
>>>>>> +++ b/drivers/media/i2c/ov5640.c
>>>>>> @@ -218,6 +218,7 @@ struct ov5640_ctrls {
>>>>>>     	struct v4l2_ctrl *test_pattern;
>>>>>>     	struct v4l2_ctrl *hflip;
>>>>>>     	struct v4l2_ctrl *vflip;
>>>>>> +	struct v4l2_ctrl *link_freq;
>>>>>>     };
>>>>>>
>>>>>>     struct ov5640_dev {
>>>>>> @@ -2198,6 +2199,10 @@ static int ov5640_try_fmt_internal(struct v4l2_subdev *sd,
>>>>>>     	return 0;
>>>>>>     }
>>>>>>
>>>>>> +static const s64 link_freq_menu_items[] = {
>>>>>> +	384000000,
>>>>>> +};
>>>>>> +
>>>>>>     static int ov5640_set_fmt(struct v4l2_subdev *sd,
>>>>>>     			  struct v4l2_subdev_pad_config *cfg,
>>>>>>     			  struct v4l2_subdev_format *format)
>>>>>> @@ -2636,6 +2641,8 @@ static int ov5640_s_ctrl(struct v4l2_ctrl *ctrl)
>>>>>>     	case V4L2_CID_VFLIP:
>>>>>>     		ret = ov5640_set_ctrl_vflip(sensor, ctrl->val);
>>>>>>     		break;
>>>>>> +	case V4L2_CID_LINK_FREQ:
>>>>>> +		return 0;
>>>>>>     	default:
>>>>>>     		ret = -EINVAL;
>>>>>>     		break;
>>>>>> @@ -2703,6 +2710,9 @@ static int ov5640_init_controls(struct ov5640_dev *sensor)
>>>>>>     				       V4L2_CID_POWER_LINE_FREQUENCY_AUTO, 0,
>>>>>>     				       V4L2_CID_POWER_LINE_FREQUENCY_50HZ);
>>>>>>
>>>>>> +	ctrls->link_freq = v4l2_ctrl_new_int_menu(hdl, ops, V4L2_CID_LINK_FREQ,
>>>>>> +						  0, 0, link_freq_menu_items);
>>>>>> +
>>>>>>     	if (hdl->error) {
>>>>>>     		ret = hdl->error;
>>>>>>     		goto free_ctrls;
>>>>>> --
>>>>>> 2.7.4
>>>>>>
>>>>>
>>>>
>>>> BR,
>>>> Hugues.
>>>
>>> --
>>> Sakari Ailus
>>> sakari.ailus@linux.intel.com
> 
> BR,
> Hugues.
> 
BR,
Hugues.