On Mon, Nov 30, 2020 at 11:06 PM Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote: > > On Mon, Nov 30, 2020 at 10:54:46PM -0800, Furquan Shaikh wrote: > > Hello Dmitry, > > > > On Mon, Nov 30, 2020 at 10:28 PM Dmitry Torokhov > > <dmitry.torokhov@xxxxxxxxx> wrote: > > > > > > Hi Furquan, > > > > > > On Mon, Nov 30, 2020 at 10:00:50PM -0800, Furquan Shaikh wrote: > > > > Raydium device does not like splitting of tx transactions into > > > > multiple messages - one for the register address and one for the > > > > actual data. This results in incorrect behavior on the device side. > > > > > > > > This change updates raydium_i2c_read and raydium_i2c_write to create > > > > i2c_msg arrays separately and passes those arrays into > > > > raydium_i2c_xfer which decides based on the address whether the bank > > > > switch command should be sent. The bank switch header is still added > > > > by raydium_i2c_read and raydium_i2c_write to ensure that all these > > > > operations are performed as part of a single I2C transfer. It > > > > guarantees that no other transactions are initiated to any other > > > > device on the same bus after the bank switch command is sent. > > > > > > i2c_transfer locks the bus [segment] for the entire time, so this > > > explanation on why the change is needed does not make sense. > > > > The actual problem is with raydium_i2c_write chopping off the write > > data into 2 messages -- one for register address and other for actual > > data. Raydium devices do not like that. Hence, this change to ensure > > that the register address and actual data are packaged into a single > > message. The latter part of the above comment attempts to explain why > > the bank switch message is added to xfer[] array in raydium_i2c_read > > and raydium_i2c_write instead of sending a separate message in > > raydium_i2c_xfer i.e. to ensure that the read/write xfer and bank > > switch are sent to i2c_transfer as a single array of messages so that > > they can be handled as an atomic operation from the perspective of > > communication with this device on the bus. > > OK, I see. > > > > > > > > > Also, does it help if you mark the data message as I2C_M_NOSTART in case > > > of writes? > > > > That is a great suggestion. I think this would be helpful in this > > scenario. Let me follow-up on this to see if it helps with the current > > problem. > > > > > > > > I also wonder if we should convert the driver to regmap, which should > > > help with handling the bank switch as well as figuring out if it can do > > > "gather write" or fall back to allocating an additional send buffer. > > > > I will start with the above suggestion and fallback to this if that > > doesn't work. > > So my understanding is that not all I2C adapters support I2C_M_NOSTART > so that is why regmap is nice as it hides it all away and figures things > on its own. > > So simple solution of I2C_M_NOSTART might be a quick fix for Chrome OS > kernel, but we'd either need to always use more expensive 2nd buffer as > is in your patch, or regmap. Ah I see. That makes sense. In that case, I think switching to regmap would be better. As you suggested, I can use I2C_M_NOSTART as a quick fix and work on enabling regmap. > > Thanks. > > -- > Dmitry
