Date:   Fri, 27 Jan 2017 11:54:40 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Kishon Vijay Abraham I <kishon@...com>
Cc:     robh+dt <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 2/4] phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom
 chips



On 01/26/2017 11:45 PM, Bjorn Andersson wrote:
> On Tue 24 Jan 01:19 PST 2017, Kishon Vijay Abraham I wrote:
>> On Monday 23 January 2017 03:43 PM, Vivek Gautam wrote:
>>> On Wed, Jan 18, 2017 at 11:33 PM, Bjorn Andersson
> [..]
>>> Yes, that's correct. The QMP and QUSB2 phy init sequences are a bunch
>>> of static values for a particular IP version. These values hardly give a
>>> meaningful data to put few phy bindings that could be referenced
>>> to configure the phy further.
>> Not really. You can have clearly defined phy binding to give meaningful data.
>> Every driver doing the same configuration bloats the driver and these
>> configuration values are just magic values which hardly can be reviewed by anyone.
>>>> Further more moving this blob to devicetree will not allow us to treat
>>>> the various QMP configurations as one HW block, as there are other
>>>> differences as well.
>>>>
>>>> Like many other drivers it's possible to create a generic version that
>>>> has every bit of logic driven by configuration from devicetree, but like
>>>> most of those cases this is not the way we split things.
>>>>
>>>> And this has the side effect of keeping the dts files human readable,
>>>> human understandable and human maintainable.
>> right. That's why I recommend having clearly defined bindings.
>> 	phy,tx-<param1> = <val, offset, mask>
>> 	phy,tx-<param2> = <val, offset, mask>
>> 	phy,tx-<param3> = <val, offset, mask>
> There's no doubt that this table needs to be encoded somewhere, so the
> question is should we hard code this in a C file or in a DTSI file.
>
> Skimming through [1] I see examples of things that differs based on how
> the specific component is integrated in a SoC or on a particular board -
> properties that are relevant to a "system integrator".
>
> As far as I can tell this blob will, if ever, only be changed by a
> driver developer and as such it's not carry information about how this
> component relates to the rest of the system and should as such not be
> part of the device tree.
>
>
> If there are properties of the hardware that is affected by how the
> component is integrated in the system I really would like for those to
> be exposed as human-readable properties that I can understand and alter
> without deep knowledge about the register map of the hardware block.

I am reaching out to our internal teams to get more information
on different possible phy configurations, based on which the registers
values are decided.
This is something that i tried to understand in the past as well, but 
couldn't
grab much information that time.
Will come back with relevant information on this.


Regards
Vivek

>> [1] -> https://www.linuxplumbersconf.org/2016/ocw/proposals/4047
> Regards,
> Bjorn
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