linux-kernel - Re: [PATCH v3 3/6] drm/rockchip/dsi: correct Feedback divider setting

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Message-ID: <39862e7a-b03f-f5d9-54db-ff9aef294a9c@st.com>
Date:   Thu, 26 Oct 2017 09:44:14 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Archit Taneja <architt@...eaurora.org>,
        Brian Norris <briannorris@...omium.org>,
        Sean Paul <seanpaul@...omium.org>
CC:     Nickey Yang <nickey.yang@...k-chips.com>,
        "mark.yao@...k-chips.com" <mark.yao@...k-chips.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "heiko@...ech.de" <heiko@...ech.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "hl@...k-chips.com" <hl@...k-chips.com>,
        "zyw@...k-chips.comg" <zyw@...k-chips.comg>,
        "xbl@...k-chips.com" <xbl@...k-chips.com>,
        "Kristian Kristensen" <hoegsberg@...il.com>
Subject: Re: [PATCH v3 3/6] drm/rockchip/dsi: correct Feedback divider setting

Hi,

On 10/26/2017 06:13 AM, Archit Taneja wrote:
> Hi,
> 
> On 10/26/2017 06:39 AM, Brian Norris wrote:
>> On Wed, Oct 25, 2017 at 03:57:19AM -0400, Sean Paul wrote:
>>> Archit asked a question about moving to
>>> dw-mipi-dsi
>>
>> That question made me think though: this approach seems backwards. It
>> seems like someone did copy/paste/fork, and then we're asking the
>> authors of the original driver to un-fork? It seems like this should
>> happen the other way around -- those trying to support a new incarnation
>> should have looked to try to abstract the original driver for their
>> uses first.
> 
> Yes, ST wanted to replicate rockchip's version of the mipi DSI driver and
> put it in their folder. If they did that, their KMS driver would have been
> the third driver to implement a third instance of the DW DSI controller 
> driver.
> Hisilicon and Rockchip being the other 2.
> 
> It was either that or attempt at a common DSI DW bridge driver. I suggested
> the latter.
> 
> The ST guys have abstracted out the PHY pieces, which they knew varied 
> between
> rockchip and ST. Ideally, they should have also tried to create a RFC 
> patch to
> make the rockchip driver use the bridge too. But they didn't do that, and
> the rockchip or hisilicon people were interested in even looking at it,
> even after I CC'ed them.
> 
>>
>> IIUC, that's exactly what Rockchip did for much of their Analogix eDP
>> code -- they reworked the Exynos DP driver to split common Analogix code
>> from any Exynos-specific bits.
> 
> I get that. I had hoped either ST or Rockchip guys would have done the 
> similar
> thing, but no one volunteered.
> 
>>
>> And actually, the current stuff in
>> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c is completely unused. It
>> exports some functions, but I see no users of it. Is that intended? Is
> 
> The ST kms driver uses it:
> 
> drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> 

I confirm STM32 chipsets use the Synopsys dw dsi bridge driver.

I plan to improve this bridge driver by adding new features (see todos + 
dsi read, command mode with bta & gpio...).

For the first commit, I did my best to keep the source code as close as 
possible to the Rockchip version, in order to ease the port for Rockchip 
guys.

>> somebody already working on refactoring existing Rockchip code to use
>> this?
> 
> I don't know. If rockchip isn't interested in doing it, we can check with
> Philippe from ST if he can try creating a RFC that converts the rockchip
> driver to use the dw-mipi-dsi driver.

I am not really interested in doing this port for Rockchip (or Hisilicon 
or i.MX...) but happy to help anyone that wants to use the dw-mipi-dsi 
bridge driver :)

Many thanks,
Philippe :)

> 
> Thanks,
> Archit
>