Re: [PATCH v2 0/2] i2c: Add new driver for Renesas RZ/V2M controller

[Philipp Zabel <p.zabel@pengutronix.de>]

Hi Geert,

On Mi, 2022-06-29 at 19:18 +0200, Geert Uytterhoeven wrote:
> Hi Philipp,
> 
> On Wed, Jun 29, 2022 at 6:21 PM Philipp Zabel <p.zabel@pengutronix.de> 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?
> 
> 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?

I would just let the reset controller driver implement this by
disabling _assert and _reset for those firmware-shared resets.

regards
Philipp