linux-kernel - Re: [PATCH 2/5] drm: of: introduce drm_of_find_panel_or

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Message-ID: <CAL_JsqJEX7=2tSP_bTq76M04G5aqCye8TnksH=HiNY+eBRAmuA@mail.gmail.com>
Date:   Mon, 6 Feb 2017 10:20:01 -0600
From:   Rob Herring <robh@...nel.org>
To:     Liviu Dudau <liviu.dudau@....com>
Cc:     David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Archit Taneja <architt@...eaurora.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Stefan Agner <stefan@...er.ch>,
        Alison Wang <alison.wang@...escale.com>,
        Xinliang Liu <z.liuxinliang@...ilicon.com>,
        Rongrong Zou <zourongrong@...il.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        CK Hu <ck.hu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Marek Vasut <marex@...x.de>,
        Mark Yao <mark.yao@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Mali DP Maintainers <malidp@...s.arm.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        Rob Clark <robdclark@...il.com>, Jyri Sarha <jsarha@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Eric Anholt <eric@...olt.net>,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH 2/5] drm: of: introduce drm_of_find_panel_or_bridge

On Mon, Feb 6, 2017 at 4:18 AM, Liviu Dudau <liviu.dudau@....com> wrote:
> On Fri, Feb 03, 2017 at 09:36:32PM -0600, Rob Herring wrote:
>> Many drivers have a common pattern of searching the OF graph for either an
>> attached panel or bridge and then finding the DRM struct for the panel
>> or bridge. Also, most drivers need to handle deferred probing when the
>> DRM device is not yet instantiated. Create a common function,
>> drm_of_find_panel_or_bridge, to find the connected node and the
>> associated DRM panel or bridge device.
>>
>> Signed-off-by: Rob Herring <robh@...nel.org>
>> ---
>>  drivers/gpu/drm/drm_of.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  include/drm/drm_of.h     | 13 +++++++++++++
>>  2 files changed, 63 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
>> index 47848ed8ca48..b29ce2f52113 100644
>> --- a/drivers/gpu/drm/drm_of.c
>> +++ b/drivers/gpu/drm/drm_of.c
>> @@ -3,7 +3,9 @@
>>  #include <linux/list.h>
>>  #include <linux/of_graph.h>
>>  #include <drm/drmP.h>
>> +#include <drm/drm_bridge.h>
>>  #include <drm/drm_crtc.h>
>> +#include <drm/drm_panel.h>
>>  #include <drm/drm_of.h>
>>
>>  static void drm_release_of(struct device *dev, void *data)
>> @@ -207,3 +209,51 @@ int drm_of_encoder_active_endpoint(struct device_node *node,
>>       return -EINVAL;
>>  }
>>  EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
>> +
>> +/*
>> + * drm_of_find_panel_or_bridge - return connected panel or bridge device
>> + * @np: device tree node containing encoder input ports
>> + * @panel: pointer to hold returned drm_panel
>> + * @bridge: pointer to hold returned drm_bridge
>> + *
>> + * Given a DT node's port and endpoint number, find the connected node and
>> + * return either the associated struct drm_panel or drm_bridge device.
>> + *
>> + * Returns zero if successful, or one of the standard error codes if it fails.
>> + */
>> +int drm_of_find_panel_or_bridge(const struct device_node *np,
>> +                             int port, int endpoint,
>> +                             struct drm_panel **panel,
>> +                             struct drm_bridge **bridge)
>> +{
>> +     int ret = -ENODEV;
>
> Given that you never return 'ret' with -ENODEV can I suggest that you initialise 'ret'
> with -EPROBE_DEFER and then you can get rid of the two assignments further down?

But I can if both panel and bridge are NULL. I'm going with Philipp's
suggestion of -EINVAL here.

Rob