AM3352: Devmem Bus error with I2C register

Seb O

Part Number: AM3352
Other Parts Discussed in Thread: TPS65218D0, , TPS65218

Dear,

I am using am3352 MCU with PMIC TPS65218D0. I2C access works properly with the i2ctool commands

I need to adjust the Thigh timing of SCL clock to meet to PMIC timing requirement.

Before to update the device tree with new timing I would to test the valeur adjusting the I2C_SCLH using the user space cli devmem(2) command.

Each time I run the command devmem or devmem2 with root user, I get the following error

>devmem 0x44E0B000

[ 4202.039491] 8<--- cut here ---
[ 4202.042605] Unhandled fault: external abort on non-linefetch (0x1018) at 0xb6f33000
[ 4202.050302] pgd = 73e506f6
[ 4202.053021] [b6f33000] *pgd=8cb4b831, *pte=44e0b383, *ppte=44e0b383

Bus error

>uname -a
Linux ######### 5.4.81 #1 PREEMPT Wed Dec 2 07:49:57 UTC 2020 armv7l GNU/Linux

How can get I2C register accessible with devmem?

Regards

Sébastien

over 4 years ago

0 Nick Saulnier over 4 years ago

TI__Guru** 105450 points

Hello Sébastien,

Why are you trying to adjust the SCL clock? Is the tsp65218 device tree node not setting up the PMIC appropriately? (documented in Linux under Documentation/devicetree/bindings/regulator/tps65218.txt )

Regards,

Nick

0 Seb O over 4 years ago in reply to Nick Saulnier

Intellectual 515 points

Dear Nick,

TPS65218D0 datasheet requires Thigh > 1us (chapter 4.6 Timing requirement)

On my design, I measure 790ns. Also note (1) below the timing table indicates the duty cycle of SCL must be > 40%

I need to to adjust it a little bit with I2C_SCLH register of AM3352.

Regards,

Sébastien

0 Nick Saulnier over 4 years ago in reply to Seb O

TI__Guru** 105450 points

Hello Sébastien,

Let's see if you and Brian can resolve your problem with circuit design first. If your thread TPS65218D0 SCL and SDA cin Capacitance cannot fix the issue, then we can restart our discussion here. I would suggest switching to 100kHz communication before trying to override Linux I2C driver settings.

Regards,

Nick

0 Seb O over 4 years ago in reply to Nick Saulnier

Intellectual 515 points

Dear Nick

The thread about the SCL and SDA Cin capacitance is another issue. It is not related to this one.

Regards,

Sébastien

0 Seb O over 4 years ago in reply to Seb O

Intellectual 515 points

I managed to fix my issue with this post.

Before to get access to I2C registor, I need to activate its clock with the devmem 0x44E004B8 l 0x2 command

Then I don't get any error using devmem on I2C0 register.

It is strange peripheral clock is deactivated while I2C-tool can access to I2C0 bus without any error!

Sébastien

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AM3352: Devmem Bus error with I2C register