AST2500 I2C problem

[Patrick Williams]

On Fri, Feb 21, 2020 at 11:42:00AM +0300, Konstantin Klubnichkin wrote:
> Hello, collegues!
>  
> I've faced a problem that don't know how to solve without tricks like overlay
> DTS.
>  
> I have PCA9555 device on I2C-11 bus, it's described in DTS as follows:
> =================================================================
> [ 3.128679] pca953x 11-0020: failed writing register
> [ 3.133860] pca953x: probe of 11-0020 failed with error -110
> [ 3.139801] aspeed-i2c-bus 1e78a400.i2c-bus: i2c bus 11 registered (dma mode),
> irq 44

Errno 110 is:
    #define	ETIMEDOUT	110	/* Connection timed out */

I think on i2c devices this happens when there is a NACK condition to
the slave address on the bus.  The odd thing here is that usually the
probing infrastructure handles the parent device (i2c bus in this case)
not being ready by returning EPROBE_DEFER in the device probe function.

Is 'bus 11' a virtual bus behind an i2c mux / switch?  It is possible
that either the driver for that switch or the pca953x driver isn't
properly handling this condition and not sending back EPROBE_DEFER.

-- 
Patrick Williams
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