From: Jani Nikula <jani.nikula@linux.intel.com>
To: Thierry Reding <treding@nvidia.com>, Lucas Stach <l.stach@pengutronix.de>
Cc: linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, a.hajda@samsung.com
Subject: Re: [RFC 0/2] drm/dsi: DSI for devices with different control bus
In-Reply-To: <20150819150207.GJ15607@ulmo.nvidia.com>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
References: <1435641851-27295-1-git-send-email-architt@codeaurora.org> <55D40F2A.6000208@codeaurora.org> <20150819131300.GC15607@ulmo.nvidia.com> <1439993828.31432.28.camel@pengutronix.de> <20150819143452.GH15607@ulmo.nvidia.com> <1439995944.31432.34.camel@pengutronix.de> <20150819150207.GJ15607@ulmo.nvidia.com>
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Date: Wed, 19 Aug 2015 18:39:30 +0300
Message-ID: <87d1yj9tjh.fsf@intel.com>
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On Wed, 19 Aug 2015, Thierry Reding <treding@nvidia.com> wrote:
> On Wed, Aug 19, 2015 at 04:52:24PM +0200, Lucas Stach wrote:
>> Am Mittwoch, den 19.08.2015, 16:34 +0200 schrieb Thierry Reding:
>> > I think that's a flawed interpretation of what's going on here. The
>> > device in fact has two interfaces: one is I2C, the other is DSI. In my
>> > opinion that's reason enough to represent it as two logical devices.
>> > 
>> Does it really have 2 control interfaces that are used at the same time?
>> Or is the DSI connection a passive data bus if the register control
>> happens through i2c?
>
> The interfaces may not be used at the same time, and the DSI interface
> may even be crippled, but the device is still addressable from the DSI
> host controller, if for nothing else than for routing the video stream.

As a drive-by comment, the Toshiba TC358764XBG/65XBG chip can be
configured via both DSI and I2C. The I2C interface requires DSI clock on
the DSI interface to operate. You may not use the interfaces
simultaneously, but provided you protect against races in register
access, both interfaces can be operational at the same time.

Sorry I couldn't find a public spec of the chip to share.

HTH,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center
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