[REGRESSION] HDMI monitor not working on Radxa Rock 5B after phy rockchip samsung hdptx HDMI 2.1 FRL patchset

Tue Feb 17 16:52:31 PST 2026

Hi Thomas,

On 2/16/26 12:48 PM, Thomas Niederprüm wrote:
> Hi Cristian,
> 
> Am Montag, dem 16.02.2026 um 03:18 +0200 schrieb Cristian Ciocaltea:
>> Hi Thomas,
>>
>> On 2/14/26 12:00 AM, Thomas Niederprüm wrote:
>>> Hi Cristian,
>>>
>>>
>>> Am Freitag, dem 13.02.2026 um 00:04 +0200 schrieb Cristian Ciocaltea:
>>>> Hi Thomas,
>>>>
>>>> On 2/11/26 11:20 PM, Thomas Niederprüm wrote:
>>>>> Hi,
>>>>>
>>>>> I'm running a Radxa Rock 5B (rk3588) on a 10+ year old Samsung TV screen
>>>>> connected via HDMI. This worked flawlessly in 6.18.7 but does not work
>>>>> on
>>>>> linux-
>>>>> next. I bisected the problem and identified commit 3481fc04 to be the
>>>>> first
>>>>> bad
>>>>> commit. This points to the phy PLL clock rate calculation to be the
>>>>> problem
>>>>> in
>>>>> connection with my monitor. As it seems relevant, I attached the EDID of
>>>>> my
>>>>> monitor.
>>>>>
>>>>> I'm booting the kernel out of EDK2 after which efifb is correctly taking
>>>>> over
>>>>> the initialized display and I can see the initial kernel boot messages
>>>>> on
>>>>> the
>>>>> HDMI output. After the drm/kms in the kernel takes over the screen
>>>>> shortly
>>>>> turns
>>>>> black, changes resolution, and then correctly displays on 6.18.7.
>>>>> However,
>>>>> in
>>>>> linux-next the screen remains black after kms took over. I cannot see
>>>>> any
>>>>> obvious differences in the boot logs but I attached two boot logs, one
>>>>> for
>>>>> the
>>>>> working 6.18.7 kernel and one for the non-working linux-next kernel.
>>>>>
>>>>> When reverting 3481fc04..de5dba83 (i.e. the faulty commit and the ones
>>>>> that
>>>>> followed in the HDMI 2.1 FRL series) I can build a working kernel from
>>>>> linux-
>>>>> next.
>>>>>
>>>>> I don't know where to dig from here but I'm happy to run any test
>>>>> necessary
>>>>> to
>>>>> track down the problem.
>>>>
>>>> It'd be helpful if you could resend the logs after booting both kernels
>>>> with
>>>> the
>>>> following params (requires CONFIG_DYNAMIC_DEBUG=y):
>>>>
>>>>   rockchipdrm.dyndbg=+p dw_hdmi_qp.dyndbg=+p
>>>> phy_rockchip_samsung_hdptx.dyndbg=+p
>>>>
>>>> As well as running the command below before connecting your display/TV:
>>>>
>>>>   $ echo 0x4 > /sys/module/drm/parameters/debug
>>>>
>>>> I've noticed you're forcing "video=HDMI-A-1:1920x1080M at 60", which should
>>>> be
>>>> anyway the preferred mode (according to the EDID).
>>>
>>> I dumped the kernel messages for a freshly built v6.19 and a linux-next
>>> image.
>>> For each kernel I booted with the suggested debug options and forcing the
>>> modes
>>> 1920x1080 at 60, 1920x1080 at 50, 1920x1080 at 30. The boot logs are attached. For
>>> v6.19
>>> all modes work. Running linux-next, 1920x1080 at 60 and 1920x1080 at 50 don't work
>>> but
>>> 1920x1080 at 30 works.
>>>
>>>> Did you try choosing a different one, e.g. 1920x1080 at 50 or 1920x1080 at 30
>>>> (they
>>>> are supported according to the listing in CTA-861 Extension Block). That's
>>>> more
>>>> a test to confirm the issue affects a particular modeline, or is more
>>>> general.
>>>>
>>>
>>> As stated above, if I force 1920x1080 at 30 the screen turns on in linux-next.
>>> 1920x1080 at 60 and 1920x1080 at 50 don't work. This points to something specific
>>> to
>>> the modeline.
>>>
>>> By diff'ing the relevant part of the logs between kernels one can see that
>>> in
>>> the cases where the screen stays black the log lacks the following lines:
>>>
>>>     rockchip-hdptx-phy fed60000.phy: rk_hdptx_ropll_tmds_cmn_config
>>> rate=185625000 mdiv=155 sdiv=4 sdm_en=1 k_sign=1 k=16 lc=62
>>>     rockchip-hdptx-phy fed60000.phy: PHY clk ready
>>>
>>> So obviously the PHY clock never gets ready.
>>>
>>> I also attached the diffs I made.
>>
>> Thanks for checking this out!  The behavior is really unexpected and I'm still
>> unable to reproduce on my end, i.e. even tested with a Samsung TV, which is
>> almost as old as yours:
>>
>>   # Mine
>>   Vendor & Product Identification:
>>     Manufacturer: SAM
>>     Model: 2685
>>     Serial Number: 1 (0x00000001)
>>     Made in: week 46 of 2012
>>
>>   # Yours
>>   Vendor & Product Identification:
>>     Manufacturer: SAM
>>     Model: 1641
>>     Serial Number: 1 (0x00000001)
>>     Made in: week 47 of 2009
>>
>> I added some more debug information, hence could you please apply commit [1]
>> on
>> your next-20260213 kernel and share the logs after testing again the
>> 1920x1080 at 50 and 1920x1080 at 30 modes?
>>
>> [1]
>> https://gitlab.collabora.com/cristicc/linux-next/-/commit/2ce4b1fb60fc601068abbe9131c05c4f09f1380c
>>
>>
> 
> Please find the logs attached.

Sorry, I somehow missed the following warning message, though it has been
already present in all the logs you've sent to me so far:

  rockchip-hdptx-phy fed60000.phy: PLL locked by unknown consumer!

That indicates the PHY has been preconfigured by an external component (e.g. the
bootloader), which is actually a scenario that I didn't verify.

However, this just another way to expose a limitation of the current approach
for managing the TMDS character rate: done via the Common Clock Framework API
instead of the HDMI PHY configuration API.

As a matter of fact, it was actually an item on my TODOs list for quite a while,
but blocked until recently due to several dependencies waiting to be merged
upstream.

Hence I took the opportunity to finalize this task - please give the following
commits in my rk3588-hdmi-debug branch [2] a try:

  07b579f28fe0 ("phy: rockchip: samsung-hdptx: Fix rate recalculation for high bpc")
  ef714855512a ("phy: rockchip: samsung-hdptx: Exclusively use PHY config API for PLL changes")

In case further debugging is necessary, you may also pick:

  1cddea39cd92 ("[DEBUG] drm/rockchip: Add HDMI verbose logging")

In the meantime, I'll do some more testing on my end.  Moreover, I'm going to
prepare a couple of additional cleanup patches (unrelated to this issue) before
sending the series out.

Regards,
Cristian

[2] https://gitlab.collabora.com/cristicc/linux-next/-/commits/rk3588-hdmi-debug