[PATCH v3 04/10] Documentations: dt-bindings: Add a document of PECI adapter driver for Aspeed AST24xx/25xx SoCs

On Tue, Apr 17, 2018 at 5:06 PM, Jae Hyun Yoo
[off-list ref] wrote:

On 4/17/2018 11:16 AM, Jae Hyun Yoo wrote:

quoted

On 4/17/2018 6:16 AM, Rob Herring wrote:

quoted

On Mon, Apr 16, 2018 at 6:12 PM, Jae Hyun Yoo
[off-list ref] wrote:

quoted

On 4/16/2018 11:10 AM, Rob Herring wrote:

quoted

On Tue, Apr 10, 2018 at 11:32:06AM -0700, Jae Hyun Yoo wrote:

quoted

This commit adds a dt-bindings document of PECI adapter driver for
Aspeed
AST24xx/25xx SoCs.

[...]

quoted

quoted

quoted

+- clocks            : Should contain clock source for PECI
controller.
+                     Should reference clkin.
+- clock_frequency   : Should contain the operation frequency of PECI
controller
+                     in units of Hz.
+                     187500 ~ 24000000

This is the frequency of the bus or used to derive it? It would be
better to specify the bus frequency instead and have the driver
calculate its internal freq. And then use "bus-frequency" instead.

I agree with you. Actually, it is being used for operation frequency
setting
of PECI controller module in SoC so it's different from the meaning of
"bus-frequency". I'll change it to "operation-frequency".

No, now you've gone from a standard property name to something custom.
Why do you need to set the frequency in DT if it is not related to the
interface frequency?

Rob

Actually, the interface frequency is affected by the operation frequency
but there is no description of its relationship in datasheet. I'll check
again about the detail to ASPEED chip vendor and will use
'bus-frequency' if available.

I investigated it more deeply. Basically, by the spec, PECI bus speed
cannot be set as a fixed speed. A PECI bus can have a wide speed range
from 2Kbps to 2Mbps which is dynamically set by a handshaking sequence
between an originator and clients called 'timing negotiation' in spec.
This timing negotiation behavior happens on every single transaction so the
bus speed also can vary on every transactions. So I'm thinking a custom
property name for it, 'peci-clk-frequency' if it is acceptable.

Okay, seems bus-frequency is not appropriate here. So use
'clock-frequency' (note the '-' not '_' as that is the standard
property).

Rob