> OK, so there are clearly restrictions to what can be written and how. >
It is hardware bug. You need to read those high PHY registers in 32-bit and modify them and write them back even though they are 16-bit. The regular low PHY registers are not affected. Another hardware bug with I2C access is an interrupt will be triggered whenever the PHY register write does not end at 32-bit boundary. Right now that interrupt is not enabled, and this problem can be easily avoided by disabling a function. These problems are for KSZ9477 only. > > My point is the driver is the only one who is using these functions to > > write, > so the developer does not try to write the register in the wrong way. > > > > It turns out the switch that requires exact 8-bit, 16-bit, and 32-bit access > functions does not work using the regmap mechanism without additional > register manipulation, so we do not really need 3 regmap pointers. > > Can you elaborate on this ? > This switch shares design with an Ethernet controller, and the register access uses byte enable. There are 4 bits of byte enable indicating whether 1 byte, 2 bytes, 3 bytes, or 4 bytes are accessed. Normally the 3 bytes option is not used. The register address is then shifted right by 2. 0x40.1 -> 0x101 0x41.1 -> 0x102 0x42.1 -> 0x104 0x43.1 -> 0x108 0x40.2 -> 0x103 0x42.2 -> 0x10c 0x40.4 -> 0x10f 0x44.4 -> 0x11f So the only option that works well with the regmap mechanism is 32-bit. Problem is the register definitions are mostly 16-bit, while the switch also shares another switch design which uses 8-bit.
