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. > > 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. Thanks for the quick response and the helpful suggestions Dmitry. I will work on these pointers and get back to you. Thanks again. - Furquan > > Thanks. > > -- > Dmitry
