linux-kernel - Re: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs to set PHY attributes

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Date:   Fri, 8 May 2020 10:50:10 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Maxime Ripard <maxime@...no.tech>,
        Swapnil Kashinath Jakhade <sjakhade@...ence.com>
CC:     Yuti Suresh Amonkar <yamonkar@...ence.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kishon@...com" <kishon@...com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jsarha@...com" <jsarha@...com>,
        "praneeth@...com" <praneeth@...com>,
        Milind Parab <mparab@...ence.com>
Subject: Re: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs to
 set PHY attributes

On 07/05/2020 20:17, Maxime Ripard wrote:

>> Actually, for this particular case, consumer driver will be the Cadence MHDP
>> bridge driver for DisplayPort which is also under review process for
>> upstreaming [1]. So this DRM bridge driver will make use of the PHY APIs
>> phy_get_bus_width() and phy_get_max_link_rate() during execution of probe
>> function to get the number of lanes and maximum link rate supported by Cadence
>> Torrent PHY. This information is required to set the host capabilities in the
>> DRM bridge driver, based on which initial values for DisplayPort link training
>> will be determined.
>>
>> The changes in this PHY patch series are based on suggestions in the review
>> comments in [1] which asks to use kernel PHY APIs to read these properties
>> instead of directly accessing PHY device node. The complete driver and actual
>> use of these APIs can be found in [2]. This is how we are planning to use
>> these APIs.
> 
> I haven't really looked into the displayport spec, but I'd assume that there's a
> lot more parameters that would need to be negociated between the phy and the DP
> block? If so, then it would make more sense to follow the path we did for
> MIPI-DSI where the parameters can be negociated through the phy_configure /
> phy_validate interface.

I don't think this is negotiation, but just exposing the (max) capabilities of PHY, inside which the 
configure can work. Maybe all the capabilities could handled with a struct (struct phy_attrs), 
instead of adding separate functions for each, though.

  Tomi

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