On Thu, Aug 27, 2020 at 05:48:48PM +0300, ext-jaakko.laine@xxxxxxxxxxx wrote: > From: Jaakko Laine <ext-jaakko.laine@xxxxxxxxxxx> > > I2C master operating in multimaster mode can get stuck > indefinitely if I2C start is detected on bus, but no master > has a transaction going. > > This is a weakness in I2C standard, which defines no way > to recover, since all masters are indefinitely disallowed > from interrupting the currently operating master. A start > condition can be created for example by an electromagnetic > discharge applied near physical I2C lines. Or a already > operating master could get reset immediately after sending > a start. > > If it is known during device tree creation that only a single > I2C master will be present on the bus, this deadlock of the > I2C bus could be avoided in the driver by ignoring the > bus_is_busy register of the xiic, since bus can never be > reserved by any other master. > > This patch adds this support for detecting single-master flag > in device tree and when provided, improves I2C reliability by > ignoring the therefore unnecessary xiic bus_is_busy register. > > Error can be reproduced by pulling I2C SDA -line temporarily low > by shorting it to ground, while linux I2C master is operating on > it using the xiic driver. The application using the bus will > start receiving linux error code 16: "Device or resource busy" > indefinitely: > > kernel: pca953x 0-0020: failed writing register > app: Error writing file, error: 16 > > With multi-master disabled device will instead receive error > code 5: "I/O error" while SDA is grounded, but recover normal > operation once short is removed. > > kernel: pca953x 0-0020: failed reading register > app: Error reading file, error: 5 > > Signed-off-by: Jaakko Laine <ext-jaakko.laine@xxxxxxxxxxx> Applied to for-next, thanks!
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