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

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Message-ID: <aDk-XKZBJiT_hJq2@pengutronix.de>
Date: Fri, 30 May 2025 07:13:00 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Lukasz Kucharczyk <lukasz.kucharczyk@...ca-geosystems.com>
Cc: stefan.eichenberger@...adex.com,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Andi Shyti <andi.shyti@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	"open list:FREESCALE IMX I2C DRIVER" <linux-i2c@...r.kernel.org>,
	"open list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <imx@...ts.linux.dev>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>,
	bsp-development.geo@...ca-geosystems.com,
	customers.leicageo@...gutronix.de
Subject: Re: [PATCH] i2c: imx: fix emulated smbus block read

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@...ca-geosystems.com>
 
Acked-by: Oleksij Rempel <o.rempel@...gutronix.de>

Thank you!

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