On 07/23/2013 10:37:46 AM, York Sun wrote:

On 07/22/2013 05:33 PM, Scott Wood wrote:

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On Mon, May 13, 2013 at 02:27:08PM -0700, York Sun wrote:

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Erratum A-006037 indicates I2C controller executes the write to =20

I2CCR only

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after it sees SCL idle for 64K cycle of internal I2C controller =20

clocks. If

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during this waiting period, I2C controller is disabled (I2CCR[MEN] =20

set to

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0), then the controller could end in bad state, and hang the =20

future access

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to I2C register.

The mpc_i2c_fixup() function tries to recover the bus from a =20

stalled state

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where the 9th clock pulse wasn't generated. However, this =20

workaround

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disables and enables I2C controller without meeting waiting =20

requirement of

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this erratum.

This erratum applies to some 85xx SoCs. It is safe to apply to all =20

of them

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for mpc_i2c_fixup().

Signed-off-by: York Sun <redacted>

---
I'd like to get rid of the #ifdef if mpc5121 is OK with the longer =20

delay.

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Are mpc5121 and mpc85xx the only things that use this?

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No. 83xx and 86xx also uses this file. But I am only unsure if mpc52xx
is OK with this extended delay. I guess they are but I don't have a
proof, or someone to confirm.
=20

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Are you sure the delay always works out to be longer?  What is the
relationship between fsl_get_sys_freq() and i2c->real_clk?

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Yes. The max divider from sys clock to i2c clcok is 32K.
i2c->real_clk is the clock I2C controller pumps out, not its internal =20
operation clock.

32K is the max for all implementations?

BTW, Where does the "2000000" come from?  Shouldn't it be 1000000 if =20
you're converting to usec?  If you're trying to add some slack, say so =20
rather than having a comment suggest that the output of that formula is =20
64K cycles.  Or is there an implicit assumption that i2c runs at half =20
the system frequency?  Is that assumption true for all implementations =20
that have this erratum?

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In any case, you should send this patch to the i2c maintainer and =20

list.

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I don't have the name on top of my head. Is that =20
linux-i2c@vger.kernel.org?

Yes, and Wolfram Sang [off-list ref] is the maintainer.  This is =20
listed in the MAINTAINERS file.

-Scott=