On Wednesday, September 10, 2014 at 05:18:06 PM, Janusz Uzycki wrote: > Reported problem: > i2cdetect scanned i2c bus very slow if address was not occupied by any > device. > > Solution: > The patch adds to mxs_i2c_pio_wait_xfer_end() function > NO_SLAVE_ACK_IRQ bit polling during wait loop (until timeout). > If the bit is set the function immediately returns ENXIO error > in order to break the loop and not reset I2C block (it is in idle state > then). The function is called by mxs_i2c_pio_setup_xfer() to wait for > complete xfer after sent SELECT, READ or WRITE command. > If SELECT command is sent and selected slave address is unused by any > device on the bus I2C block sets NO_SLAVE_ACK_IRQ flag and doesn't > deassert CTRL0_RUN. Therefore we need to break the timeout loop when the > flag is set, > otherwise the loop continues until long timeout (1000ms). > The change does not affect READ command because slave does not ack > any byte then (only the master does ack / or not for the last read byte). > According to i.MX28 reference manual (quoted below) it is not clear > if the patch affects WRITE command. However when no acked bytes > on WRITE command followed after address byte (SELECT command) > STAT_GOT_A_NAK flag is set rather than NO_SLAVE_ACK_IRQ (no tested). > Therefore clock stretching shouldn't be affected too. > It has confirmation in FSL BSP 2.6.35 i2c implementation which > completes xfer after NO_SLAVE_ACK_IRQ interrupt and scheduled work. > Registers on NO_SLAVE_ACK_IRQ in PIO mode: > * STAT: 0xd0000e00 > MASTER_PRESENT > SLAVE_PRESENT > GOT_A_NAK ! > BUS_BUSY > CLK_GEN_BUSY > DATA_ENGINE_BUSY > * CTRL0: 0x20230000 > RUN ! > RETAIN_CLOCK > MASTER_MODE > DIRECTION > * CTRL1: 0x688600a0 > RD_QUEUE_IRQ > WR_QUEUE_IRQ > ACK_MODE > SLAVE_ADDRESS_BYTE=0b10000110 > BUS_FREE_IRQ > NO_SLAVE_ACK_IRQ ! > > NO_SLAVE_ACK_IRQ (CTRL1): > When a start condition is transmitted in master mode, the next byte > contains an address for a targeted slave. If the targeted slave does not > acknowledge the address byte, then this interrupt is set, no further I2C > protocol is processed, and the I2C bus returns to the idle state. > This bit is set to indicate that an interrupt is requested > by the I2C controller because the slave addressed > by a master transfer did not respond with an acknowledge. > > Signed-off-by: Janusz Uzycki <j.uzycki@xxxxxxxxxxxxxx> OK, uh, can the commit message not be shortened to like 5-10 lines ? I think you really need to find your balance when it comes to documenting changes, but don't worry, this will happen sooner rather than later ;-) It would be sufficient to say that you had problem with slow i2cdetect and that was because the i2c controller driver ignored the NO_SLAVE_ACK bit. By leveraging NO_SLAVE_ACK bit, the speedup happens. And this change is correct and doesn't break anything because <a few lines here>. Do you know what I mean ? -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
