Messages in this thread | | | Date | Fri, 8 Oct 2021 13:27:53 +0300 | From | Laurent Pinchart <> | Subject | Re: [PATCH v5 2/6] phy: cdns-dphy: Add Rx support |
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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 ?
> > 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
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