Messages in this thread | | | Subject | Re: [RFC PATCH 0/2] Clause-22/Clause-45 MDIO regmap support | From | Sander Vanheule <> | Date | Mon, 07 Jun 2021 14:06:26 +0200 |
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Hi Mark,
On Mon, 2021-06-07 at 12:54 +0100, Mark Brown wrote: > On Fri, Jun 04, 2021 at 08:16:53PM +0200, Sander Vanheule wrote: > > On Fri, 2021-06-04 at 18:25 +0100, Mark Brown wrote: > > > > I think these registers are in practice going to either need to be > > > volatile (how most of them work at the minute) or otherwise handled in > > > regmap (eg, the page support we've got). Having two different names for > > > the same register feels like it's asking for bugs if any of the higher > > > level functions of regmap get used. > > > This is actually an issue with a GPIO chip that I'm trying to implement [1]. > > To > > set an output, data is written to the register. To get an input value, data > > is > > read from the register. Since a register contains data for 16 GPIO lines, a > > regular read-modify-write could erroneously overwrite output values. A pin > > outside of the RMW mask could've changed to an input, and may now be reading > > a > > different value. The issue I was running into, had to do with a RMW not > > being > > written because the pin value apparently hadn't changed. > > If the hardware isn't able to read back the status of the pins in output > mode (even if it's always reading back from the input circuit where is > it getting other inputs from?) you're probably better off with just > having an open coded cache separately than trying to make up fake > registers that rely on current implementation details to work. > > > I didn't use the existing paging mechanism for this, since (I think) then I > > would need to specify a register that contains the page index. But as I > > don't > > have an actual page register, I would have to specify another existing > > register > > with an empty mask. This could lead to useless bus activity if I > > accidentally > > chose a volatile register. > > This is clearly not paging, it would be totally inappropraite to use > paging for this.
Thank you for the input. I'll take this to the RTL8231 thread, to see what I can come up with as a cleaner solution, without abusing the regmap interface.
Best regards, Sander
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