[PATCH v5 1/2] drm/bridge: Add Cadence DSI driver

Boris Brezillon boris.brezillon at free-electrons.com
Mon Jan 29 14:16:21 UTC 2018


On Mon, 29 Jan 2018 15:59:33 +0200
Tomi Valkeinen <tomi.valkeinen at ti.com> wrote:

> On 29/01/18 15:14, Boris Brezillon wrote:
> 
> >> You don't disable the dsi_sys_clk neither in the ok nor in the error paths.  
> > 
> > Hm, it shouldn't be enabled in the first place: the runtime resume
> > hook takes care of enabling it, and we don't need this clock to access
> > IP registers (which is all we do in the probe).  
> 
> Ah, right, you can just use pm_runtime directly to enable the IP.
> 
> I was looking at the docs, but it wasn't quite clear to me when exactly
> dsi_sys_clk is needed. I take it that you can access registers with just
> the dsi_p_clk, but you can't really do anything with the IP without
> dsi_sys_clk? If so, I think enabling both dsi_p_clk and dsi_sys_clk in
> the runtime PM callbacks is ok.

That's my understanding.

> 
> Alternatively, if dsi_sys_clk is only needed for some specific
> functionality, a more correct way would be to enable that clock only
> when that operation is performed.

IIUC, it's needed to clock the PPI domain, so any operation
transmitting things on the DSI bus requires the sys clock.


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