Hi Philipp, Geert, On 29 June 2022 18:18 Geert Uytterhoeven wrote: > On Wed, Jun 29, 2022 at 6:21 PM Philipp Zabel wrote: > > On Di, 2022-06-28 at 20:45 +0100, Phil Edworthy wrote: > > > The Renesas RZ/V2M SoC (r9a09g011) has a new i2c controller. This > series > > > add the driver. One annoying problem is that the SoC uses a single > reset > > > line for two i2c controllers, and unfortunately one of the controllers > > > is managed by some firmware, not by Linux. Therefore, the driver just > > > deasserts the reset. > > > > This sounds scary. If the driver is never loaded, and the reset is > > never deasserted, what happens to the firmware trying to access the > > other i2c controller? Does it hang? Or write to the reset controller > > registers to deassert the reset? If so, is there any protection against > > concurrent access from firmware and reset controller driver? Where a common reset is used by Linux and some firmware, I think we have to ensure/assume that both only ever de-assert it. In this particular SoC, the register used to assert/de-assert the reset has write enable bits in the upper half of the reg. There shouldn't be any issues with both trying to de-assert the reset at the same time. > In response to v1, I wrote > > | That is actually an integration issue, not an i2c controller issue. > | > | Perhaps we need a RESET_IS_CRITICAL flag, cfr. CLK_IS_CRITICAL, > | to be set by the reset provider? >From what I understand, there are two main use cases for resets: 1. Often reset lines may be asserted at power on and so a driver needs to de-assert them so that the module can be used. 2. A driver may need to reset the module for some reason. I have only seen this with watchdog timers with no way out. So if a driver does not need to reset the module, shouldn't the driver only ever be de-asserting the reset line? If so, it also doesn’t matter whether the reset is shared with other modules or not. If a driver needs to reset the module, then the reset cannot be shared with other modules used by firmware or Linux, or we cannot use any other modules that share the reset line. Have I missed something? Thanks Phil
