> > Here (and also in sii902x_i2c_bypass_deselect) you do a rmw access to the > > SII902X_SYS_CTRL_DATA register without coordinating with regmap. Regmap is > > also doing rmw accesses to that register in other parts of the driver. I > > think you need to either add comment as to why that is safe (maybe other > > things make it impossible for the two rmw accesses to cross?), or add the > > missing coordination. > > > > The other two places where SII902X_SYS_CTRL_DATA is being handled are > sii902x_bridge_disable and sii902x_bridge_enable, I didn’t think there is > any chance of the modes being probed while the bridge gets enabled/disabled, > but now that you make me think about it user space may trigger the readback > of the EDID at the most inconvenient times. Anyway, this is a good point, and > since I don't think I am supposed to access regmap's lock from outside the APIs, > I could switch to the unlocked version of update_bits from within sii902x_bridge_disable > and sii902x_bridge_enable, and manually grab the i2c adapter lock, what do you think? > The bridge enable/disable callbacks deal with different bits of register SII902X_SYS_CTRL_DATA, and the value of register SII902X_SYS_CTRL_DATA after sii902x_i2c_bypass_deselect is the same as when sii902x_i2c_bypass_select gets triggered so basically even if we managed to get in the way of the regmap rmw (in the sense that for example sii902x_bridge_enable reads SII902X_SYS_CTRL_DATA and then we call into sii902x_i2c_bypass_select) by the time regmap_update_bits can perform the write operation the value of register SII902X_SYS_CTRL_DATA is the same as the one read by regmap, as "select xfer deselect" won't alter the final value of SII902X_SYS_CTRL_DATA and nobody can get in between. What do you think I should do? Do you think I can leave this alone and maybe add some comments or do you think I should explicitly protect access to SII902X_SYS_CTRL_DATA? Thanks, Fab Renesas Electronics Europe Ltd, Dukes Meadow, Millboard Road, Bourne End, Buckinghamshire, SL8 5FH, UK. Registered in England & Wales under Registered No. 04586709.
