linux-kernel - Re: [PATCH v5 4/5] drm: imx: Add i.MX 6 MIPI DSI host platform driver

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Date:   Tue, 31 Mar 2020 01:05:39 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     Adrian Ratiu <adrian.ratiu@...labora.com>
Cc:     "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sjoerd Simons <sjoerd.simons@...labora.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Martyn Welch <martyn.welch@...labora.com>,
        Jonas Karlman <jonas@...boo.se>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        Emil Velikov <emil.velikov@...labora.com>,
        linux-rockchip@...ts.infradead.org,
        NXP Linux Team <linux-imx@....com>, kernel@...labora.com,
        linux-stm32@...md-mailman.stormreply.com,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH v5 4/5] drm: imx: Add i.MX 6 MIPI DSI host platform
 driver

On Tue, 2020-03-31 at 00:31 +0300, Adrian Ratiu wrote:
> On Mon, 30 Mar 2020, Ezequiel Garcia <ezequiel@...labora.com> 
> wrote:
> > Hello Fabio, Adrian: 
> > 
> > On Mon, 2020-03-30 at 08:49 -0300, Fabio Estevam wrote: 
> > > Hi Adrian,  On Mon, Mar 30, 2020 at 8:34 AM Adrian Ratiu 
> > > <adrian.ratiu@...labora.com> wrote: 
> > > > This adds support for the Synopsis DesignWare MIPI DSI v1.01 
> > > > host controller which is embedded in i.MX 6 SoCs.   Based on 
> > > > following patches, but updated/extended to work with existing 
> > > > support found in the kernel:  - drm: imx: Support Synopsys 
> > > > DesignWare MIPI DSI host controller 
> > > >   Signed-off-by: Liu Ying <Ying.Liu@...escale.com> 
> > > >  - ARM: dtsi: imx6qdl: Add support for MIPI DSI host 
> > > > controller 
> > > >   Signed-off-by: Liu Ying <Ying.Liu@...escale.com> 
> > >  This one looks like a devicetree patch, but this patch does 
> > > not touch devicetree.  
> > > > +       ret = clk_prepare_enable(dsi->pllref_clk); +       if 
> > > > (ret) { +               dev_err(dev, "%s: Failed to enable 
> > > > pllref_clk\n", __func__); +               return ret; + 
> > > > } + +       dsi->mux_sel = 
> > > > syscon_regmap_lookup_by_phandle(dev->of_node, "fsl,gpr"); + 
> > > > if (IS_ERR(dsi->mux_sel)) { +               ret = 
> > > > PTR_ERR(dsi->mux_sel); +               dev_err(dev, "%s: 
> > > > Failed to get GPR regmap: %d\n", + 
> > > > __func__, ret); +               return ret; 
> > >  You should disable the dsi->pllref_clk clock prior to 
> > > returning the error.  
> > 
> > Another approach could be moving the clock on and off to to 
> > component_ops.{bind,unbind} (as rockhip driver does). 
> > 
> > What exactly is the PLL clock needed for? Would it make sense to 
> > move it some of the PHY power on/off? (Maybe not, but it's 
> > worthing checking). 
> > 
> > Also, it seems the other IP blocks have this PLL clock, so maybe 
> > it could be moved to the dw_mipi_dsi core? This could be 
> > something for a follow-up, to avoid creeping this series.
> 
> Hi Ezequiel,
> 
> pll is the video reference clock which drives the data lanes and 
> yes all drivers have it as it's a basic requirement, so moving it 
> to the common bridge is indeed a good idea, however this kind of 
> driver refactoring is out of scope for this specific patch series, 
> because, for now, I'd like to get the regmap and the imx6 driver 
> in, once that is done we can think how to further abstract away 
> common logic and slim down the existing drivers further.
> 
> Basically I just want to avoid feature creep as I expect v6 to be 
> ~ 8 patches big and the series is already over 1200 lines.
> 

Oh, absolutely: if there's one thing I try to avoid is
feature creep -- together with bikeshedding!

Do note however, that you could move the PLL clock handling
to component_ops.{bind,unbind} and maybe simplify the error
handling.

(BTW, great work!)

Cheers,
Ezequiel