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

From: Tomi Valkeinen <tomi.valkeinen@ti.com>
To: Maxime Ripard <maxime@cerno.tech>,
	Swapnil Kashinath Jakhade <sjakhade@cadence.com>
Cc: Yuti Suresh Amonkar <yamonkar@cadence.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kishon@ti.com" <kishon@ti.com>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"jsarha@ti.com" <jsarha@ti.com>,
	"praneeth@ti.com" <praneeth@ti.com>,
	Milind Parab <mparab@cadence.com>
Subject: Re: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs to set PHY attributes
Date: Fri, 8 May 2020 10:50:10 +0300	[thread overview]
Message-ID: <f6e0566a-8e15-5c55-3167-6a1526c37be7@ti.com> (raw)
In-Reply-To: <20200507171738.atzyfpueo6bjbwpb@gilmour.lan>

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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