linux-kernel - Re: [PATCH] reset: socfpga: use arch

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Date:	Thu, 9 Oct 2014 09:57:49 -0500
From:	atull <atull@...nsource.altera.com>
To:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
CC:	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	Philipp Zabel <p.zabel@...gutronix.de>, <dinh.linux@...il.com>,
	<grant.likely@...aro.org>, <robh+dt@...nel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] reset: socfpga: use arch_initcall for early
 initialization

On Thu, 9 Oct 2014, Steffen Trumtrar wrote:

> On Thu, Oct 09, 2014 at 08:16:18AM -0500, Dinh Nguyen wrote:
> > Hi Philipp,
> > 
> > On 10/9/14, 4:03 AM, Philipp Zabel wrote:
> > > Am Mittwoch, den 08.10.2014, 21:44 -0500 schrieb
> > > dinguyen@...nsource.altera.com:
> > >> From: Dinh Nguyen <dinguyen@...nsource.altera.com>
> > >>
> > >> There are certain drivers that are required to get loaded very early using
> > >> arch_initcall. An example of such a driver is the SOCFPGA's FPGA bridge driver.
> > >> This driver has to get loaded early because it needs to enable FPGA components
> > >> that are connected to the bridge.
> > >>
> > >> This FPGA bridge driver will using the reset controller API to toggle it's
> > >> reset bits, thus, it needs the reset driver to be loaded as early as possible
> > >> in order for it to get used properly.
> > > 
> > > Without knowing the details, this sounds like the wrong approach. Can't
> > > the bridge driver return -EPROBE_DEFER until the reset controller is
> > > available?
> > > 

I don't think we can do deferred probing for arch_initcall.

> > 
> > The bridge driver is also using arch_initcall, as it also needs to get
> > loaded early for FPGA IPs to work, and so later driver loading will work
> > for the FPGA IPs.
> > 
> 
> For the bridge driver the same is true. I guess that there *might* be
> IP cores where you need to be very early, but that shouldn't be the normal
> case. If the driver can't get loaded properly, the right thing would be to
> fix the driver.

Some fpga ip drivers will need to be early (and will assume that the fpga
was programmed by the bootloader).  We want to support that case.

> 
> I have developed a bridge driver, too (which only needs the devicetree binding
> docu for a v1) and I have a driver+IP core that is directly connected to the
> bridge. I don't need any messing around with the initcalls to work properly.
> -EPROBE_DEFER works just fine.

Is this based on the "proposed fpga bridge framework" that I posted?
What we are trying to do is update that bridge driver to use the reset driver for 
submitting v2.

Alan

> 
> What I do need however is loading the FPGA very early of course, if it is not
> done in the bootloader.
> 
> Regards,
> Steffen
> 
> -- 
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