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

Lukasz Kucharczyk posted 1 patch 7 months ago 
drivers/i2c/busses/i2c-imx.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
[PATCH] i2c: imx: fix emulated smbus block read
Posted by Lukasz Kucharczyk 7 months ago 
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>
---
 drivers/i2c/busses/i2c-imx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index ee0d25b498cb..4bf550a3b98d 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -1008,7 +1008,7 @@ static inline int i2c_imx_isr_read(struct imx_i2c_struct *i2c_imx)
 	/* setup bus to read data */
 	temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
 	temp &= ~I2CR_MTX;
-	if (i2c_imx->msg->len - 1)
+	if ((i2c_imx->msg->len - 1) || (i2c_imx->msg->flags & I2C_M_RECV_LEN))
 		temp &= ~I2CR_TXAK;
 
 	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
@@ -1063,6 +1063,7 @@ static inline void i2c_imx_isr_read_block_data_len(struct imx_i2c_struct *i2c_im
 		wake_up(&i2c_imx->queue);
 	}
 	i2c_imx->msg->len += len;
+	i2c_imx->msg->buf[i2c_imx->msg_buf_idx++] = len;
 }
 
 static irqreturn_t i2c_imx_master_isr(struct imx_i2c_struct *i2c_imx, unsigned int status)
-- 
2.34.1
Re: [PATCH] i2c: imx: fix emulated smbus block read
Posted by Andi Shyti 5 months, 3 weeks ago 
Hi Lukasz,

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>

merged to i2c/i2c-host-fixes.

Thanks,
Andi
Re: [PATCH] i2c: imx: fix emulated smbus block read
Posted by Oleksij Rempel 6 months, 3 weeks ago 
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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Re: [PATCH] i2c: imx: fix emulated smbus block read
Posted by Stefan Eichenberger 6 months, 3 weeks ago 
Hi Lukasz,

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>
> ---
>  drivers/i2c/busses/i2c-imx.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index ee0d25b498cb..4bf550a3b98d 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -1008,7 +1008,7 @@ static inline int i2c_imx_isr_read(struct imx_i2c_struct *i2c_imx)
>  	/* setup bus to read data */
>  	temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
>  	temp &= ~I2CR_MTX;
> -	if (i2c_imx->msg->len - 1)
> +	if ((i2c_imx->msg->len - 1) || (i2c_imx->msg->flags & I2C_M_RECV_LEN))
>  		temp &= ~I2CR_TXAK;
>  
>  	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> @@ -1063,6 +1063,7 @@ static inline void i2c_imx_isr_read_block_data_len(struct imx_i2c_struct *i2c_im
>  		wake_up(&i2c_imx->queue);
>  	}
>  	i2c_imx->msg->len += len;
> +	i2c_imx->msg->buf[i2c_imx->msg_buf_idx++] = len;
>  }
>  
>  static irqreturn_t i2c_imx_master_isr(struct imx_i2c_struct *i2c_imx, unsigned int status)

This makes sense, we never tested the actual SMBus emulation. Thanks a lot for the fix.

Reviewed-by: Stefan Eichenberger <eichest@gmail.com>

Patchew 2.1-devel-b67e4c2

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