[PATCH v7 00/10] Add falcon support for am62a, 62p and 62x

[Francesco Valla]

Hi Vignesh,

Il 2025-07-01 09:14 Raghavendra, Vignesh ha scritto:
> Hi Francesco
> 
> On 6/30/2025 7:35 PM, Francesco Valla wrote:
>> Hi Anshul,
>> 
>> On Tuesday, 3 June 2025 at 16:24:40 Anshul Dalal <anshuld at ti.com> 
>> wrote:
>>> This patch set adds support for falcon boot on AM62a, 62p and 62x by
>>> bypassing A53 SPL and U-boot.
>>> 
>>> Existing Boot flow:
>>> R5 SPL -> ATF -> A53 SPL -> U-Boot -> Linux Kernel
>>> 
>>> Updated flow:
>>> R5 SPL -> ATF -> Linux Kernel
>>> 
>>> ...
>> 
>> I tried this series on a custom device based on AM62P. While it's 
>> working
>> mostly fine, I noticed that PWM0 is not working after a falcon boot 
>> from
>> R5F, while it was working correctly after a boot through full U-Boot.
>> 
>> After a bit of debugging, I noticed that the epwm_tbclk0 is marked as
>> disabled in hardware in debugfs's clk_summary even if enabled by 
>> software:
>> 
>>  $ head -n 2 /sys/kernel/debug/clk/clk_summary && cat 
>> /sys/kernel/debug/clk/clk_summary | grep pwm
>> 
>>                                  enable  prepare  protect              
>>                   duty  hardware                            connection
>>    clock                          count    count    count        rate  
>>  accuracy phase  cycle    enable   consumer                         id
>>  clk:86:0                            0       0        0        
>> 250000000   0          0     50000      Y   23000000.pwm               
>>      fck
>>  epwm_tbclk2                         0       0        0        0       
>>     0          0     50000      N   deviceless                      
>> no_connection_id
>>  epwm_tbclk1                         0       0        0        0       
>>     0          0     50000      N   deviceless                      
>> no_connection_id
>>  epwm_tbclk0                         1       1        0        0       
>>     0          0     50000      N   23000000.pwm                    
>> tbclk
>> 
>> 
>> Reading the associated register (0x00104130) returns in fact 
>> 0x00000000,
>> while writing to it has no effect (and after a write the register 
>> reads
>> back as 0x00000000).
>> 
>> 
>> Do you have any idea on the reason of this behaviour? I don't think it 
>> is
>> directly related to the Falcon boot implementation, but probably a 
>> side
>> effect of it (maybe something that was enabled by A53 SPL?).
>> 
> 
> My guess is that CTRL_MMR region which hosts TB_CLKEN isn't unlocked.
> 
> We unlock the CTRL_MMR here:
> https://elixir.bootlin.com/u-boot/v2025.04/source/arch/arm/mach-k3/am62px/am62p5_init.c#L156
> 
> But its possible that DM firmware that runs after R5 SPL re-locks these
> registers and Linux is no longer able to write to those registers.
> So this may need fix in the DM firmware to keep these regions unlocked.
> 
> Looking at address of tbclk (0x00104130), it should be under region 4.
> Could you try after running the equivalent of
> mmr_unlock(CTRL_MMR0_BASE, 4); at Linux prompt using devmem2 and then 
> modify the TB_CLKEN?
> 

that was exactly the issue, after unlocking the CTRL_MMR region the
TB_CLKEN bits wrote correctly and the PWM started working again.
According to TRM, the correct region is number 1.

These were the issued commands to unlock the CTRL_MMR region 1:

  $ devmem2 0x105008 w 0x68EF3490
  $ devmem2 0x10500C w 0xD172BC5A

and then to write TB_CLKEN for PWM channel 0:

  $ devmem2 0x00104130 w 0x1

The clock then is marked as enabled also from a hardware point of view:

  $ head -n 2 /sys/kernel/debug/clk/clk_summary && cat 
/sys/kernel/debug/clk/clk_summary | grep pwm

                                  enable  prepare  protect                
                 duty  hardware                            connection
    clock                          count    count    count        rate   
accuracy phase  cycle    enable   consumer                         id
  epwm_tbclk2                         0       0        0        0         
   0          0     50000      Y   deviceless                      
no_connection_id
  epwm_tbclk1                         0       0        0        0         
   0          0     50000      N   deviceless                      
no_connection_id
  epwm_tbclk0                         1       1        0        0         
   0          0     50000      N   23000000.pwm                    tbclk
  clk:86:0                            0       0        0        250000000 
   0          0     50000      Y   23000000.pwm                    fck


What's the correct path to issue a bug for the DM firmware?

Thank you!

Regards,
Francesco