On Tue, Aug 17, 2021 at 9:51 AM zhiyong.tao <zhiyong.tao@xxxxxxxxxxxx> wrote:
> In one chip, If GPIO is different, the MTXXXX_PULL_UP_RSEL_001 may
> means different actual bias resistance setting.
>
> For example,
>
> KPROW IO
> Paramters Descriptions Min Typ Max
> UNIT
> Rpd Input pull-down resistance 40 75 190 Kohm
> Rpu Input pull-up resistance 40 75 190 Kohm
> Rpd Input pull-down resistance 0.8 1.6 2 Kohm
> Rpu Input pull-up resistance 0.8 1.6 2 Kohm
This is exactly why we should try to use SI units in the device tree.
I assume that the software can eventually configure which resistance
it gets?
The electronics people will say make sure it is pulled down by around
80 kOhm, they can put that on the device tree and your code can
say, "hm 40 < 80 < 190 this is OK" and let the value pass.
We do not define these exact semantics, it is up to the driver code
to decide what to do with the Ohm value 80000 in this case, but
it makes perfect sent for me to let it pass and fail if someone
for example requests 20 kOhm, or at least print a helpful warning:
dev_warn(dev, "the requested resistance %d is out of range, supported
range %d to %d kOhm\n",
val, low, high);
This is what makes the SI units really helpful for people writing device
trees: solve real integration tasks and make it easy to do the right thing.
Yours,
Linus Walleij
