linux-kernel - Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev driver

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Message-ID: <e9076980-ce84-f9ee-096d-865243b82a9e@gmail.com>
Date:   Thu, 9 Feb 2017 15:51:47 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, kernel@...gutronix.de,
        fabio.estevam@....com, mchehab@...nel.org, hverkuil@...all.nl,
        nick@...anahar.org, markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, bparrot@...com,
        geert@...ux-m68k.org, arnd@...db.de, sudipm.mukherjee@...il.com,
        minghsiu.tsai@...iatek.com, tiffany.lin@...iatek.com,
        jean-christophe.trotin@...com, horms+renesas@...ge.net.au,
        niklas.soderlund+renesas@...natech.se, robert.jarzmik@...e.fr,
        songjun.wu@...rochip.com, andrew-ct.chen@...iatek.com,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev
 driver



On 02/09/2017 03:49 PM, Steve Longerbeam wrote:
>
>
> On 02/08/2017 03:42 PM, Russell King - ARM Linux wrote:
>> On Wed, Feb 08, 2017 at 03:23:53PM -0800, Steve Longerbeam wrote:
>>>> Actually, this exact function already exists as 
>>>> dw_mipi_dsi_phy_write in
>>>> drivers/gpu/drm/rockchip/dw-mipi-dsi.c, and it looks like the D-PHY
>>>> register 0x44 might contain a field called HSFREQRANGE_SEL.
>>> Thanks for pointing out drivers/gpu/drm/rockchip/dw-mipi-dsi.c.
>>> It's clear from that driver that there probably needs to be a fuller
>>> treatment of the D-PHY programming here, but I don't know where
>>> to find the MIPI CSI-2 D-PHY documentation for the i.MX6. The code
>>> in imxcsi2_reset() was also pulled from FSL, and that's all I really 
>>> have
>>> to go on for the D-PHY programming. I assume the D-PHY is also a
>>> Synopsys core, like the host controller, but the i.MX6 manual doesn't
>>> cover it.
>> Why exactly?  What problems are you seeing that would necessitate a
>> more detailed programming of the D-PHY?  From my testing, I can wind
>> a 2-lane MIPI bus on iMX6D from 912Mbps per lane down to (eg) 308Mbps
>> per lane with your existing code without any issues.
>
> That's good to hear.
>
> Just from my experience with struggles to get the CSI2 receiver
> up and running with an active clock lane, and my suspicions that
> some of that could be due to my lack of understanding of the D-PHY
> programming.

But I should add that after a re-org of the sequence, it looks more stable
now. Tested on both the SabreSD and SabreLite with the OV5640.

Steve