From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Pratyush Yadav <p.yadav@ti.com>, Vinod Koul <vkoul@kernel.org>,
Vignesh Raghavendra <vigneshr@ti.com>,
Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>,
Nikhil Devshatwar <nikhil.nd@ti.com>,
Chunfeng Yun <chunfeng.yun@mediatek.com>,
Kishon Vijay Abraham I <kishon@ti.com>,
Rob Herring <robh+dt@kernel.org>,
linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org
Subject: Re: [PATCH v5 2/6] phy: cdns-dphy: Add Rx support
Date: Fri, 8 Oct 2021 14:55:54 +0200 [thread overview]
Message-ID: <YWA/2o/Df34VDcpp@aptenodytes> (raw)
In-Reply-To: <YWAdKTvYzF58oyU/@pendragon.ideasonboard.com>
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Hi,
On Fri 08 Oct 21, 13:27, Laurent Pinchart wrote:
> Hi Pratyush,
>
> On Thu, Oct 07, 2021 at 05:44:38PM +0530, Pratyush Yadav wrote:
> > On 07/10/21 03:10AM, Laurent Pinchart wrote:
> > > On Fri, Oct 01, 2021 at 11:53:16AM +0530, Vinod Koul wrote:
> > > > On 17-09-21, 22:58, Pratyush Yadav wrote:
> > > > > On 16/09/21 12:22PM, Paul Kocialkowski wrote:
> > > > > > On Fri 03 Sep 21, 00:25, Pratyush Yadav wrote:
> > > > > > > The Cadence DPHY can be used to receive image data over the CSI-2
> > > > > > > protocol. Add support for Rx mode. The programming sequence differs from
> > > > > > > the Tx mode so it is added as a separate set of hooks to isolate the two
> > > > > > > paths. The mode in which the DPHY has to be used is selected based on
> > > > > > > the compatible.
> > > > > >
> > > > > > I just realized that I didn't follow-up on a previous revision on the debate
> > > > > > about using the phy sub-mode to distinguish between rx/tx.
> > > > > >
> > > > > > I see that you've been using a dedicated compatible, but I'm not sure this is a
> > > > > > good fit either. My understanding is that the compatible should describe a group
> > > > > > of register-compatible revisions of a hardware component, not how the hardware
> > > > > > is used specifically. I guess the distinction between rx/tx falls under
> > > > > > the latter rather than the former.
> > > > >
> > > > > I am not sure if that is the case. For example, we use "ti,am654-ospi"
> > > > > for Cadence Quadspi controller. The default compatible, "cdns,qspi-nor",
> > > > > only supports Quad SPI (4 lines). The "ti,am654-ospi" compatible also
> > > > > supports Octal SPI (8 lines).
> > > >
> > > > Those are hardware defaults right?
> > > >
> > > > > In addition, I feel like the Rx DPHY is almost a different type of
> > > > > device from a Tx DPHY. The programming sequence is completely different,
> > > >
> > > > Is that due to direction or something else..?
> > > >
> > > > > the clocks required are different, etc. So I think using a different
> > > > > compatible for Rx mode makes sense.
> > > >
> > > > Is the underlaying IP not capable of both TX and RX and in the specific
> > > > situations you are using it as TX and RX.
> > > >
> > > > I am okay that default being TX but you can use Paul's approach of
> > > > direction with this to make it better proposal
> > >
> > >
> > > Given that the RX and TX implementations are very different (it's not a
> > > matter of selecting a mode at runtime), I'm actually tempted to
> > > recommend having two drivers, one for the RX PHY and one for the TX PHY.
> > > This can only be done with two different compatible strings, which I
> > > think would be a better approach.
> >
> > FWIW, I think having different drivers would certainly make things
> > easier to maintain.
>
> I'm sorry for not having recommended this in the first place.
>
> Any objection from anyone against going in this direction ?
So apparently there is not a single register that is shared between rx and tx
and clocks are not the same either so it feels to me like a separate driver
would be legit. This looks like two distinct IPs sharing the same base address.
Cheers,
Paul
> > > It's unfortunate that the original compatible string didn't contain
> > > "tx". We could rename it and keep the old one in the driver for backward
> > > compatibility, making things cleaner going forward.
>
> --
> Regards,
>
> Laurent Pinchart
--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com
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next prev parent reply other threads:[~2021-10-08 12:56 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-02 18:55 [PATCH v5 0/6] Rx mode support for Cadence DPHY Pratyush Yadav
2021-09-02 18:55 ` [PATCH v5 1/6] phy: cdns-dphy: Prepare for Rx support Pratyush Yadav
2021-10-07 0:02 ` Laurent Pinchart
2021-09-02 18:55 ` [PATCH v5 2/6] phy: cdns-dphy: Add " Pratyush Yadav
2021-09-16 10:22 ` Paul Kocialkowski
2021-09-17 17:28 ` Pratyush Yadav
2021-09-28 16:35 ` Pratyush Yadav
2021-10-01 6:23 ` Vinod Koul
2021-10-01 8:07 ` Pratyush Yadav
2021-10-07 0:10 ` Laurent Pinchart
2021-10-07 12:14 ` Pratyush Yadav
2021-10-08 10:27 ` Laurent Pinchart
2021-10-08 12:55 ` Paul Kocialkowski [this message]
2021-10-25 8:09 ` Vinod Koul
2021-09-02 18:55 ` [PATCH v5 3/6] phy: dt-bindings: Convert Cadence DPHY binding to YAML Pratyush Yadav
2021-09-02 18:55 ` [PATCH v5 4/6] phy: dt-bindings: cdns,dphy: make clocks optional for Rx mode Pratyush Yadav
2021-09-07 19:02 ` Rob Herring
2021-10-06 23:57 ` Laurent Pinchart
2021-09-02 18:55 ` [PATCH v5 5/6] phy: dt-bindings: cdns,dphy: add power-domains property Pratyush Yadav
2021-09-02 18:55 ` [PATCH v5 6/6] phy: dt-bindings: cdns,dphy: add Rx DPHY compatible Pratyush Yadav
2021-09-07 19:03 ` Rob Herring
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