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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E53D4C43381 for ; Thu, 21 Mar 2019 18:00:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B5219218A2 for ; Thu, 21 Mar 2019 18:00:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728749AbfCUSAr convert rfc822-to-8bit (ORCPT ); Thu, 21 Mar 2019 14:00:47 -0400 Received: from unicorn.mansr.com ([81.2.72.234]:56096 "EHLO unicorn.mansr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725985AbfCUSAr (ORCPT ); Thu, 21 Mar 2019 14:00:47 -0400 Received: by unicorn.mansr.com (Postfix, from userid 51770) id 2C02914CEB; Thu, 21 Mar 2019 18:00:45 +0000 (GMT) From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= To: Maxime Ripard Cc: David Airlie , Chen-Yu Tsai , dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/sun4i: hdmi: add support for ddc-i2c-bus property References: <20190311134713.25876-1-mans@mansr.com> <20190311154702.eslw5ccol44vxcmy@flea> <20190314154105.o6r7hzeuiyajxh7v@flea> <20190318155013.lge2x2cp5hvyz52f@flea> <20190319123445.w6q7vzr3qtgkejwj@flea> <20190321154452.noq3l44x3mshljvy@flea> Date: Thu, 21 Mar 2019 18:00:45 +0000 In-Reply-To: <20190321154452.noq3l44x3mshljvy@flea> (Maxime Ripard's message of "Thu, 21 Mar 2019 16:44:52 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Maxime Ripard writes: > On Tue, Mar 19, 2019 at 12:48:19PM +0000, Måns Rullgård wrote: >> Maxime Ripard writes: >> >> > On Mon, Mar 18, 2019 at 04:23:56PM +0000, Måns Rullgård wrote: >> >> Maxime Ripard writes: >> >> >> >> > On Thu, Mar 14, 2019 at 04:09:13PM +0000, Måns Rullgård wrote: >> >> >> Maxime Ripard writes: >> >> >> >> >> >> > On Mon, Mar 11, 2019 at 04:11:06PM +0000, Måns Rullgård wrote: >> >> >> >> Maxime Ripard writes: >> >> >> >> >> >> >> >> > Hi! >> >> >> >> > >> >> >> >> > On Mon, Mar 11, 2019 at 01:47:13PM +0000, Mans Rullgard wrote: >> >> >> >> >> Sometimes it is desirabled to use a separate i2c controller for ddc >> >> >> >> >> access. This adds support for the ddc-i2c-bus property of the >> >> >> >> >> hdmi-connector node, using the specified controller if provided. >> >> >> >> >> >> >> >> >> >> Signed-off-by: Mans Rullgard >> >> >> >> >> --- >> >> >> >> >> drivers/gpu/drm/sun4i/sun4i_hdmi.h | 1 + >> >> >> >> >> drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 37 +++++++++++++++++++++++--- >> >> >> >> >> 2 files changed, 35 insertions(+), 3 deletions(-) >> >> >> >> >> >> >> >> >> >> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi.h b/drivers/gpu/drm/sun4i/sun4i_hdmi.h >> >> >> >> >> index b685ee11623d..b08c4453d47c 100644 >> >> >> >> >> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi.h >> >> >> >> >> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi.h >> >> >> >> >> @@ -269,6 +269,7 @@ struct sun4i_hdmi { >> >> >> >> >> struct clk *tmds_clk; >> >> >> >> >> >> >> >> >> >> struct i2c_adapter *i2c; >> >> >> >> >> + struct i2c_adapter *ddc_i2c; >> >> >> >> >> >> >> >> >> >> /* Regmap fields for I2C adapter */ >> >> >> >> >> struct regmap_field *field_ddc_en; >> >> >> >> >> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c >> >> >> >> >> index 061d2e0d9011..5b2fac79f5d6 100644 >> >> >> >> >> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c >> >> >> >> >> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c >> >> >> >> >> @@ -212,7 +212,7 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector) >> >> >> >> >> struct edid *edid; >> >> >> >> >> int ret; >> >> >> >> >> >> >> >> >> >> - edid = drm_get_edid(connector, hdmi->i2c); >> >> >> >> >> + edid = drm_get_edid(connector, hdmi->ddc_i2c ?: hdmi->i2c); >> >> >> >> > >> >> >> >> > You can't test whether ddc_i2c is NULL or not... >> >> >> >> > >> >> >> >> >> if (!edid) >> >> >> >> >> return 0; >> >> >> >> >> >> >> >> >> >> @@ -228,6 +228,28 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector) >> >> >> >> >> return ret; >> >> >> >> >> } >> >> >> >> >> >> >> >> >> >> +static struct i2c_adapter *sun4i_hdmi_get_ddc(struct device *dev) >> >> >> >> >> +{ >> >> >> >> >> + struct device_node *phandle, *remote; >> >> >> >> >> + struct i2c_adapter *ddc; >> >> >> >> >> + >> >> >> >> >> + remote = of_graph_get_remote_node(dev->of_node, 1, -1); >> >> >> >> >> + if (!remote) >> >> >> >> >> + return ERR_PTR(-EINVAL); >> >> >> >> >> + >> >> >> >> >> + phandle = of_parse_phandle(remote, "ddc-i2c-bus", 0); >> >> >> >> >> + of_node_put(remote); >> >> >> >> >> + if (!phandle) >> >> >> >> >> + return NULL; >> >> >> >> >> + >> >> >> >> >> + ddc = of_get_i2c_adapter_by_node(phandle); >> >> >> >> >> + of_node_put(phandle); >> >> >> >> >> + if (!ddc) >> >> >> >> >> + return ERR_PTR(-EPROBE_DEFER); >> >> >> >> >> + >> >> >> >> >> + return ddc; >> >> >> >> > >> >> >> >> > ... Since even in (most) error cases you're returning a !NULL pointer. >> >> >> >> > >> >> >> >> >> +} >> >> >> >> >> + >> >> >> >> >> static const struct drm_connector_helper_funcs sun4i_hdmi_connector_helper_funcs = { >> >> >> >> >> .get_modes = sun4i_hdmi_get_modes, >> >> >> >> >> }; >> >> >> >> >> @@ -575,6 +597,12 @@ static int sun4i_hdmi_bind(struct device *dev, struct device *master, >> >> >> >> >> goto err_disable_mod_clk; >> >> >> >> >> } >> >> >> >> >> >> >> >> >> >> + hdmi->ddc_i2c = sun4i_hdmi_get_ddc(dev); >> >> >> >> >> + if (IS_ERR(hdmi->ddc_i2c)) { >> >> >> >> >> >> >> >> ... which is checked here. >> >> >> >> >> >> >> >> The property is optional, so the idea was to return null in that case >> >> >> >> and use the built-in controller. If the property exists but some error >> >> >> >> occurs, we want to abort rather than proceed with the fallback which >> >> >> >> almost certainly won't work. >> >> >> >> >> >> >> >> Maybe I got something wrong in that logic. >> >> >> > >> >> >> > Indeed, I just got confused. I guess returning ENODEV in such a case, >> >> >> > and testing for that, would make things more obvious. >> >> >> >> >> >> There's also a case I hadn't thought of: property exists but isn't a >> >> >> valid phandle. What do you think is the correct action in that case? >> >> > >> >> > I think we would have that one covered. of_parse_phandle will return >> >> > !NULL, but then of_get_i2c_adapter_by_node will return NULL since we >> >> > wouldn't have an associated i2c adapter to the bogus phandle, and you >> >> > are checking for that already. >> >> >> >> of_parse_phandle() doesn't differentiate between a missing property and >> >> an existing non-phandle value. The following cases are possible with >> >> this patch: >> >> >> >> - ddc-i2c-bus points to valid i2c controller node: use this for ddc >> >> - no ddc-i2c-bus property: return NULL, use internal i2c >> >> - ddc-i2c-bus exists but isn't a phandle: likewise >> >> - ddc-i2c-bus points to a non-i2c-controller node: EPROBE_DEFER >> >> >> >> The last two cases obviously mean the devicetree is invalid, so perhaps >> >> it doesn't matter much what happens then. I don't think it's possible >> >> to distinguish between a well-formed phandle pointing to some bogus node >> >> and a good one where the i2c driver hasn't been probed yet. >> > >> > Ah, I see what you mean now. Yeah, there's not much we can do against >> > a wrong / corrupted DT. The DT validation would help prevent the third >> > case, and possibly the fourth, but that's basically the only thing we >> > can do. >> >> We need to return -EPROBE_DEFER in the case that everything is fine but >> the i2c driver hasn't been probed yet. From here, that is >> indistinguishable from of_parse_phandle() returning a completely bogus >> node. > > That's unfortunate, but if we start to not trust the DT content, we > have far worse to deal with. > >> If the ddc-i2c-bus property doesn't contain a phandle at all, we could >> either return an error or fall back to the internal i2c. The patch does >> the latter because that's less code. I don't think that's any worse >> than aborting entirely in terms of user experience. > > I'm totally fine with the latter behaviour as well. And like I said, > the DT validation can help us prevent that case from happening > entirely at compilation time. Well, do you want any changes to the patch or not? -- Måns Rullgård