On Tue, 10 Dec 2024 13:47:25 +0800 Yu-Hsian Yang <j2anfernee@xxxxxxxxx> wrote: > Dear Jonathan Cameron, > > Sorry the above mail is not finished and just sent it. > I would explain why we can't use bulk read sequential bytes in our chips. Ah! I replied to previous. Let me see what you added. > > > > + > > > > + guard(mutex)(&chip->access_lock); > > > > + err = regmap_read(chip->regmap, REG_CHANNEL_ENABLE_1, &value); > > > > + if (err < 0) > > > > + return err; > > > > + data[0] = (u8)value; > > > > + > > > > + err = regmap_read(chip->regmap, REG_CHANNEL_ENABLE_2, &value); > > > > + if (err < 0) > > > > + return err; > > > > > > Here I think you can use a bulk read as the registers are next to each other. > > > > > > Generally, registers with 8 bits support Byte format, and registers > with more than 8 bits support Word format. > If transmission a Word command to a register that supports Byte > format, the second byte will get 0xFF. > Here, if we use regmap_bulk_read(), we would get first byte correct > and second byte is wrong 0xff. > > I use i2ctransfer command to demo it. > root@evb-npcm845:~# i2ctransfer -f -y 5 w1@0x1d 0x13 r1 > 0xff > root@evb-npcm845:~# i2ctransfer -f -y 5 w1@0x1d 0x14 r1 > 0x0f > > root@evb-npcm845:~# i2ctransfer -f -y 5 w1@0x1d 0x13 r2 > 0xff 0xff > And if we read four bytes, you can see the first and third byte as we wanted. > root@evb-npcm845:~# i2ctransfer -f -y 5 w1@0x1d 0x13 r4 > 0xff 0xff 0x0f 0xff > > so we can't use bulk read directly since it would get a second byte 0xff. > The safe method is to use read byte twice. That command does not do the same thing as regmap_bulk_read() will here. It will issue a series of byte reads. Jonathan
