Messages in this thread | | | Date | Tue, 28 Jun 2022 13:03:14 +0300 | From | Andy Shevchenko <> | Subject | Re: [PATCH 5/8] dt_bindings: rs485: Correct delay values |
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On Thu, Jun 23, 2022 at 10:17:06PM +0200, Lino Sanfilippo wrote: > On 23.06.22 at 18:29, Andy Shevchenko wrote: > > On Wed, Jun 22, 2022 at 05:46:56PM +0200, Lino Sanfilippo wrote: > >> > >> The maximum allowed delay for RTS before and RTS after send is 100 ms. > >> Adjust the documentation accordingly. > > > > Is it only documentation issue? If the code allows this to be set higher > > than 100, we may not change the documentation since this an ABI (from > > firmware <--> kernel perspective) we need to support old variants. > > Well currently the documentation claims that a maximum of 1000 msecs is allowed but > nothing actually checks the values read from device tree/ACPI and so it is possible > to set much higher values (note that the UART drivers dont check the delays read from > DT/ACPI either, the only exception I found is max310x which clamps it to 15 ms). > > We already have a maximum of 100 ms defined for RTS delays set via TIOCSRS485. To be > consistent with TIOCSRS485 the same limit is used for DT/ACPI values in this patch. > > I am aware that this changes the firmware/kernel ABI. But we had a similar situation when > the sanity checks for TIOCSRS485 were introduced > (see https://lore.kernel.org/all/20220410104642.32195-2-LinoSanfilippo@gmx.de/) > since before we did not have those limits for all drivers (some drivers clamped the > values itself but many did not care). > Furthermore 100 ms is already a very high value for RTS delays (which are usually rather > in usecs range). So IMHO the risk is very low to break anything when values are clamped > that are higher than that.
You need to elaborate all this in the commit message to justify the change.
-- With Best Regards, Andy Shevchenko
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