Re: [PATCH] i2c-qoriq: modified compatibility for correct prescaler

On Wed, 2014-10-29 at 09:59 +0100, Valentin Longchamp wrote:

On 10/29/2014 12:08 AM, Scott Wood wrote:

quoted

On Fri, 2014-10-17 at 11:27 +0200, Valentin Longchamp wrote:

quoted

With "fsl-i2c" compatibility the i2c frequency is not set
correctly, because it sets no prescaler. According to the AN2919 from
Freescale and the QorIQ (P2041) documentation, the source clock is 1/2
the platform clock. This implies that a prescaler of 2 must be used.

This changes the compatibility of the qoriq-i2c .dtsi files to pick the
mpc8543, which uses the same driver but sets the correct prescaler.

Signed-off-by: Rainer Boschung <redacted>
Signed-off-by: Valentin Longchamp <redacted>
---

 arch/powerpc/boot/dts/fsl/qoriq-i2c-0.dtsi | 4 ++--
 arch/powerpc/boot/dts/fsl/qoriq-i2c-1.dtsi | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/boot/dts/fsl/qoriq-i2c-0.dtsi b/arch/powerpc/boot/dts/fsl/qoriq-i2c-0.dtsi
index 5f9bf7d..aa6c366 100644
--- a/arch/powerpc/boot/dts/fsl/qoriq-i2c-0.dtsi
+++ b/arch/powerpc/boot/dts/fsl/qoriq-i2c-0.dtsi

@@ -36,7 +36,7 @@ i2c@118000 {
 	#address-cells = <1>;
 	#size-cells = <0>;
 	cell-index = <0>;
-	compatible = "fsl-i2c";
+	compatible = "fsl,mpc8543-i2c", "fsl-i2c";
 	reg = <0x118000 0x100>;
 	interrupts = <38 2 0 0>;
 	dfsrr;

@@ -46,7 +46,7 @@ i2c@118100 {
 	#address-cells = <1>;
 	#size-cells = <0>;
 	cell-index = <1>;
-	compatible = "fsl-i2c";
+	compatible = "fsl,mpc8543-i2c", "fsl-i2c";
 	reg = <0x118100 0x100>;
 	interrupts = <38 2 0 0>;
 	dfsrr;

Are all chips that use this dtsi 100% compatible with mpc8543's i2c, or
just in ways the Linux driver cares about?

I have just looked briefly at the mpc8548 RM (covers mpc8543) and its i2c
controller looks the same as the qoriq's. I cannot however state if they are
100% compatible.

If we wanted to be on the safe side and strict (since we are not sure that the
hardware is 100% compatible), we maybe should add a fsl,qoriq-i2c compatible to
the driver that does the same as mpc8543-i2c.

If we're going to change the device tree I'd rather just add a property
to say what the prescaler is.

-Scott