From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 683F0C433EF for ; Fri, 8 Oct 2021 10:28:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CDC061027 for ; Fri, 8 Oct 2021 10:28:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239742AbhJHKaD (ORCPT ); Fri, 8 Oct 2021 06:30:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230032AbhJHKaA (ORCPT ); Fri, 8 Oct 2021 06:30:00 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2896C061570 for ; Fri, 8 Oct 2021 03:28:05 -0700 (PDT) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 3D187581; Fri, 8 Oct 2021 12:28:03 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1633688883; bh=O/OYayj1ukIAB3FdcOduo8Ue4fDcLxGu5RhxJwuFdC4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=wFFVrO633mz76kUAGqZCu/F3OOKQS1ZNBkMG4QklxdKxXoI2j65I6mFVOgx5/NiyR yWtoKRuj7zhS/PfJUby+szUoAgr2WgdEQEQFAIR7/15njlT9H7Fw+M2vQXzhGPBO4o PG8VnU6KuG+nqmsri3fyHRxPJCp9Uh0FFLV98gU0= Date: Fri, 8 Oct 2021 13:27:53 +0300 From: Laurent Pinchart To: Pratyush Yadav Cc: Vinod Koul , Paul Kocialkowski , Vignesh Raghavendra , Tomi Valkeinen , Nikhil Devshatwar , Chunfeng Yun , Kishon Vijay Abraham I , Rob Herring , linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org Subject: Re: [PATCH v5 2/6] phy: cdns-dphy: Add Rx support Message-ID: References: <20210902185543.18875-1-p.yadav@ti.com> <20210902185543.18875-3-p.yadav@ti.com> <20210917172809.rjtf7ww7vjcfvey5@ti.com> <20211007121436.jkck2cue5zd3rys4@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20211007121436.jkck2cue5zd3rys4@ti.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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