On Monday, September 22, 2014 at 04:33:49 PM, Janusz Użycki wrote: > W dniu 2014-09-19 04:45, Marek Vasut pisze: > > 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 ? > > Yes, I know. It was explanation in details rather for comments than > final patch. > Is it ok?: > i2cdetect scanned i2c bus slow because the i2c-mxs driver ignored the > NO_SLAVE_ACK bit > during busy-waiting loop. Thanks to the patch, the speedup happens. > The change doesn't break anything else because: > - on SELECT: NO_SLAVE_ACK bit checking is just welcome > - on READ: master (the i2c controller, no slave device) generates > ACK/NAK bit > - on WRITE: NO_SLAVE_ACK can be treated as NAK (the same effect) > so even the i2c controller sets NO_SLAVE_ACK on NAK (not confirmed) > the WRITE is not effected > - on clock stretching: SCL wire is involved, it has no influence > on the ACK bit value on SDA wire I think Wolfram already patched the commit message, no ? -- 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
