[U-Boot] omap24xx_i2c: i2c 16-bit write to pcf8575

[U-Boot] omap24xx_i2c: i2c 16-bit write to pcf8575

[Richard Retanubun]

Hello,

My platform is a dra7xx_evm. My code baseline is denx master

I am trying to write to the pcf8575 i2c gpio expander at address 0x21 (bit P4)

I can read 16-bit okay in this version, but 16-bit writing is not working.

// Display current values
i2c md 21 0.0 2
0000: f7 eb    ..

// Set bit P4 to 1
i2c mw 21 0.0 0xffeb 2

// But it remains at 0xf7
i2c md 21 0.0 2
0000: f7 eb    ..

When we put scopes on the i2c lines, it seems that the i2c mw
transaction produces a longer i2c bus sequence that does not map to
the [Start:Addr:W:A:P7-P0:A:P17-P10:A:Stop] that the pcf8575 device
expects.

Either I am invoking "i2c mw" incorrectly, or the oma24xx_i2c driver
is not handling i2c 16-bit writes correctly yet.

Any hints will be appreciated. Thanks for everyone's time

-- Richard Retanubun

[U-Boot] omap24xx_i2c: i2c 16-bit write to pcf8575

[Tom Rini]

On Wed, Mar 05, 2014 at 04:01:47PM -0500, Richard Retanubun wrote:

> Hello,
> 
> My platform is a dra7xx_evm. My code baseline is denx master
> 
> I am trying to write to the pcf8575 i2c gpio expander at address 0x21 (bit P4)
> 
> I can read 16-bit okay in this version, but 16-bit writing is not working.
> 
> // Display current values
> i2c md 21 0.0 2
> 0000: f7 eb    ..
> 
> // Set bit P4 to 1
> i2c mw 21 0.0 0xffeb 2
> 
> // But it remains at 0xf7
> i2c md 21 0.0 2
> 0000: f7 eb    ..
> 
> When we put scopes on the i2c lines, it seems that the i2c mw
> transaction produces a longer i2c bus sequence that does not map to
> the [Start:Addr:W:A:P7-P0:A:P17-P10:A:Stop] that the pcf8575 device
> expects.
> 
> Either I am invoking "i2c mw" incorrectly, or the oma24xx_i2c driver
> is not handling i2c 16-bit writes correctly yet.
> 
> Any hints will be appreciated. Thanks for everyone's time

Have you tried doing it progmatically rather than via the command line?
You may indeed be running into something we don't support in "i2c mw",
if I skim the comments right.

-- 
Tom
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