Re: GPIO state in qemu

[Rashmica Gupta <rashmica.g@gmail.com>]

On Mon, 2019-09-09 at 19:02 +0200, Cédric Le Goater wrote:
> On 09/09/2019 18:20, James Feist wrote:
> > On 9/6/19 11:05 AM, Joel Stanley wrote:
> > > At the osfc hackathon today James and I were talking about Qemu's
> > > new support for modelling GPIOs. Here's some documentation on how
> > > it can be used.
> > > 
> > > To set a pin's state in the monitor:
> > > 
> > > qom-set gpio gpioA0 true
> > > 
> > > To do the equivalent in code:
> > > 
> > > object_property_set_bool(OBJECT(&s->gpio), true, "gpioA0",
> > > &error_abort);
> > 
> > I'm trying to use object_property_set_bool in hw/arm/aspeed.c in an
> > i2c_init block and I'm noticing by the time uboot is reached that
> > the registers are reset back to the default. 
> 
> These routines are called before the machine and devices are reseted.
> 
> > If I use qom-set it seems to work correctly. 
> 
> The machine has been reseted.
> 
> > Where is the correct place to put the object_property_set_bool so
> > that it doesn't get reset by the time it's ready to be read? Does
> > AspeedBoardConfig need a gpio_init as well as an i2c_init?
>  
> we would need to change the default reset value in the reset handler
> of the GPIO device model : aspeed_gpio_reset(). We don't have a way 
> to set default values yet, all 0s for now.
> 
> Rashmica,
> 
> Would it be complex to add a set of default values with which we 
> could memset the ->sets array in the reset handler() like we do 
> for SCU ? 
>

I think it should be pretty straightforward. Do we want one statically
defined set of default values per SoC version?

> Having a different set of default values per machine would require 
> a second set of properties under AspeedGPIOState and some slight 
> rework of aspeed_gpio_get/set_pin.
> 

Why would it require rework of get/set pin?

> Didn't you have a patch for reset tolerant values some time ago ? 
>  

Yes, but it was a bit hacky and I didn't have a good way to test it. We
need to share a property with the wdt and differentiate between a SoC
reset, full system reset and a full wdt reset. Iirc we only use the
reset tolerant values for a SoC reset? I assume we would want to set
the default values for all three types of reset?



> Thanks,
> 
> C.