Re: [PATCH] i2c: imx: fix emulated smbus block read

Oleksij Rempel
2025-05-30T05:13:20Z

On Tue, May 20, 2025 at 02:22:52PM +0200, Lukasz Kucharczyk wrote:
> Acknowledge the byte count submitted by the target.
> When I2C_SMBUS_BLOCK_DATA read operation is executed by
> i2c_smbus_xfer_emulated(), the length of the second (read) message is set
> to 1. Length of the block is supposed to be obtained from the target by the
> underlying bus driver.
> The i2c_imx_isr_read() function should emit the acknowledge on i2c bus
> after reading the first byte (i.e., byte count) while processing such
> message (as defined in Section 6.5.7 of System Management Bus
> Specification [1]). Without this acknowledge, the target does not submit
> subsequent bytes and the controller only reads 0xff's.
>
> In addition, store the length of block data obtained from the target in
> the buffer provided by i2c_smbus_xfer_emulated() - otherwise the first
> byte of actual data is erroneously interpreted as length of the data
> block.
>
> [1] https://smbus.org/specs/SMBus_3_3_20240512.pdf
>
> Fixes: 5f5c2d4579ca ("i2c: imx: prevent rescheduling in non dma mode")
> Signed-off-by: Lukasz Kucharczyk <lukasz.kucharczyk@leica-geosystems.com>

Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>

Thank you!

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