Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <e2b5efc4-1b2d-191f-e4ee-5ad7a64c63cd@denx.de>
Date:   Tue, 4 Apr 2023 01:12:48 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.9.0
Subject: Re: [PATCH v1 1/2] dt-bindings: display: bridge: sn65dsi83: Add DSI
 video mode
To:     Francesco Dolcini <francesco@dolcini.it>,
        Rob Herring <robh@kernel.org>
Cc:     Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Robert Foss <rfoss@kernel.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        dri-devel@lists.freedesktop.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        devicetree@vger.kernel.org,
        Francesco Dolcini <francesco.dolcini@toradex.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>, linux-kernel@vger.kernel.org
References: <20230330101752.429804-1-francesco@dolcini.it>
 <20230330101752.429804-2-francesco@dolcini.it>
 <20230403210622.GA1740065-robh@kernel.org>
 <ZCtB8Vu4Brm3G639@francesco-nb.int.toradex.com>
Content-Language: en-US
From:   Marek Vasut <marex@denx.de>
In-Reply-To: <ZCtB8Vu4Brm3G639@francesco-nb.int.toradex.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 4/3/23 23:15, Francesco Dolcini wrote:
> On Mon, Apr 03, 2023 at 04:06:22PM -0500, Rob Herring wrote:
>> On Thu, Mar 30, 2023 at 12:17:51PM +0200, Francesco Dolcini wrote:
>>> From: Francesco Dolcini <francesco.dolcini@toradex.com>
>>>
>>> SN65DSI8[34] device supports burst video mode and non-burst video mode
>>> with sync events or with sync pulses packet transmission as described in
>>> the DSI specification.
>>>
>>> Add property to select the expected mode, this allows for example to
>>> select a mode that is compatible with the DSI host interface.
>>
>> Why does this need to be in DT?
> 
>> The source and sink drivers should know what their capabilities are
>> and pick the best common one.
> 
> Is there a best mode?

I think yes:
Burst (is better than) Sync Events (is better than) Sync Pulses

Burst is most energy efficient, Sync-Pulses is the simplest and least 
energy efficient and with most constraints.

> Isn't this a decision how do we want the 2 peers
> to communicate?

I don't think so, I believe the Host and nearest bridge should be able 
to negotiate their capabilities (mode, link rate, etc.) within the DRM 
subsystem.

> For the MIPI-DSI Linux/DRM experts: am I missing something? Is there
> another way to have a DSI video sink to ask for a specific mode?

I'm afraid this is not implemented yet, so ... plumbing needed.

[...]