linux-kernel - Regression: at24 eeprom writing

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Date:	Sat, 3 Oct 2015 01:05:21 +0200
From:	Peter Rosin <peda@...ator.liu.se>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Wolfram Sang <wsa@...-dreams.de>,
	Christian Gmainer <christian.gmeiner@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Ludovic Desroches <ludovic.desroches@...el.com>
Subject: Regression: at24 eeprom writing

Hi!

I recently upgraded from the atmel linux-3.18-at91 kernel to vanilla 4.2
and everything seemed fine. Until I tried to write to the little eeprom
chip. I then tried the linux-4.1-at91 kernel and that suffers too.

The symptoms are that it seems like writes get interrupted, and restarted
again without properly initializing everything again. Inspecting the i2c
bus during these fails gets me something like this (int hex) when I

echo abcdefghijklmnopqr > /sys/bus/i2c/devices/0-0050/eeprom

S a0 00 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 70 P
S a0 10 (clk and data low for a "long" time) 10 71 72 0a P

Notice how the address byte in the second chunk (10) is repeated after
the strange event on the i2c bus.

I looked around and found that if I revert a839ce663b3183209fdf7b1fc4796bfe2a4679c3
"eeprom: at24: extend driver to allow writing via i2c_smbus_write_byte_data"
eeprom writing starts working again.

AFAICT, the i2c-at91 bus driver makes the eeprom driver use the
i2c_transfer code path both with that patch and with it reverted,
so I sadly don't see why the patch makes a difference.

I'm on a board that is based on the sama5d31 evaluation kit, with a
NXP SE97BTP,547 chip and this in the devicetree:

			i2c0: i2c@...14000 {
				status = "okay";

				jc42@18 {
					compatible = "jc42";
					reg = <0x18>;
				};

				eeprom@50 {
					compatible = "24c02";
					reg = <0x50>;
					pagesize = <16>;
				};
			};

Any ideas?

Cheers,
Peter
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