[Letux-kernel] Strange problem with non-LPAE letux-4.20-rc kernels on 4GB Pyra only

H. Nikolaus Schaller hns at goldelico.com
Fri Dec 7 15:52:54 CET 2018


> Am 07.12.2018 um 15:16 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> 
>> Am 07.12.2018 um 12:09 schrieb Andreas Kemnade <andreas at kemnade.info>:
>> 
>> On Fri, 7 Dec 2018 09:22:12 +0100
>> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>> 
>> [...]
>>> This pin has a 100k pullup to 1.8V and 800mV is a typical symptom that
>>> the gpio pin does have a pull-down enabled and not a pull-up or internal
>>> pull disabled..
>>> 
>> And this 800mV has probably a big tolerance, so depending on the phase of the
>> moon or something like that, it might work or not.
>> I had the sd card disappearing here once. I just thought it was an adapter
>> problem but it is probably just the voltage level at that pin.
> 
> Indeed...
> 
> After doing
> 
> 	/usr/bin/arm-linux-gnueabihf/devmem2 0x4a002974 w 0x11e011e
> 
> SD card insertion/removal is detected and I can measure 0V <-> 1.8V voltage swing
> on the CD input.
> 
> The value after boot is 0x1060106 which matches (omap5-letux-cortex15-v5.3.dts):
> 
> /* the hardware bug of earlier releases has been fixed and
> * external pull-up for gpio8_228 and gpio8_229 is installed.
> * Hence we can disable pullup/down.
> */
> 
> &mmc1_pins {
> 	pinctrl-single,pins = <
> 		OMAP5_IOPAD(0x174, PIN_INPUT | MUX_MODE6)	/* 0x174:[15:0] sdcard_cd/gpio8_228 */
> 		OMAP5_IOPAD(0x176, PIN_INPUT | MUX_MODE6)	/* 0x175:[31:16] sdcard_wp/gpio8_229 */
> 	>;
> };
> 
> Therefore, it is not a pinmux issue.
> 
> Hm. But why is the pull-down enabled or the external pull-up not effective if we define PIN_INPUT only?
> 
> And it still does not explain the difference between 4.19 and 4.20 kernels.
> 
> Maybe the 4.19 kernel does more polling of the mmc interface to detect than 4.20.
> While 4.20 only relies on proper CD gpio?

Note: this DTS file seems to have been introduced with 4.19-rc1 / 4.18.1.

> 
> And maybe the pull-up resisor isn't soldered properly. So it might be a mix of HW and SW
> changes which happened to come in parallel...
> 
> Anyways I can't simply fix it in SW by adding INPUT_PULLUP if it is a HW issue of this single unit.
> 
> BR,
> Nikolaus
> 
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