linux-kernel - Re: [LINUX PATCH 2/2] drm: xlnx: dsi: driver for Xilinx DSI Tx subsystem

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Message-ID: <YqZY4QMAkGiFOOWE@pendragon.ideasonboard.com>
Date:   Mon, 13 Jun 2022 00:21:37 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Venkateshwar Rao Gannavarapu 
        <venkateshwar.rao.gannavarapu@...inx.com>, airlied@...ux.ie,
        vgannava@...inx.com, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [LINUX PATCH 2/2] drm: xlnx: dsi: driver for Xilinx DSI Tx
 subsystem

Hi Sam,

On Fri, May 13, 2022 at 01:05:06PM +0200, Sam Ravnborg wrote:
> On Thu, May 12, 2022 at 07:23:13PM +0530, Venkateshwar Rao Gannavarapu wrote:
> > The Xilinx MIPI DSI Tx Subsystem soft IP is used to display video
> > data from AXI-4 stream interface.
> > 
> > It supports upto 4 lanes, optional register interface for the DPHY
> > and multiple RGB color formats.
> > This is a MIPI-DSI host driver and provides DSI bus for panels.
> > This driver also helps to communicate with its panel using panel
> > framework.
> 
> Thanks for submitting this driver. I have added a few comments in the
> following that I hope you will find useful to improve the driver.
> 
> > Signed-off-by: Venkateshwar Rao Gannavarapu <venkateshwar.rao.gannavarapu@...inx.com>
> > ---
> >  drivers/gpu/drm/xlnx/Kconfig    |  14 ++
> >  drivers/gpu/drm/xlnx/Makefile   |   1 +
> >  drivers/gpu/drm/xlnx/xlnx_dsi.c | 456 ++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 471 insertions(+)
> >  create mode 100644 drivers/gpu/drm/xlnx/xlnx_dsi.c

[snip]

> > diff --git a/drivers/gpu/drm/xlnx/xlnx_dsi.c b/drivers/gpu/drm/xlnx/xlnx_dsi.c
> > new file mode 100644
> > index 0000000..a5291f3
> > --- /dev/null
> > +++ b/drivers/gpu/drm/xlnx/xlnx_dsi.c

[snip]

> > +static inline void xlnx_dsi_writel(void __iomem *base, int offset, u32 val)
> > +{
> > +	writel(val, base + offset);
> > +}
> > +
> > +static inline u32 xlnx_dsi_readl(void __iomem *base, int offset)
> > +{
> > +	return readl(base + offset);
> > +}
> 
> When I see implementations like this I wonder if a regmap would be
> beneficial?

regmap often seems overkill to me when the driver only needs plain
32-bit mmio read/write, given the overhead it adds at runtime. Is it
just me ?

[snip]

-- 
Regards,

Laurent Pinchart