From mboxrd@z Thu Jan  1 00:00:00 1970
From: u.kleine-koenig@pengutronix.de (Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=)
Date: Fri, 13 Aug 2010 10:17:20 +0200
Subject: [PATCH v2] mx35: Fix boot ROM hang in internal boot mode
In-Reply-To: <20100812121504.GC8670@local>
References: <20100811233721.GB6411@local>
	<20100812055753.GB9763@pengutronix.de>
	<20100812112938.GB8670@local> <20100812121504.GC8670@local>
Message-ID: <20100813081720.GA23898@pengutronix.de>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Aug 12, 2010 at 02:15:04PM +0200, Hans J. Koch wrote:
> On Thu, Aug 12, 2010 at 01:29:40PM +0200, Hans J. Koch wrote:
> > On Thu, Aug 12, 2010 at 07:57:53AM +0200, Uwe Kleine-K?nig wrote:
> > > > +	}
> > > > +
> > > > +	__raw_writel(cgr2, CCM_BASE + CCM_CGR2);
> > > > +	__raw_writel(cgr3, CCM_BASE + CCM_CGR3);
> > > Note that my question concerning the UART clock was less about UART1 vs
> > > UART0 but more if the ROM really needs a UART clock.
> > 
> > In my tests on an mx35pdk board, I found these three clocks being the
> > minimum set of additional clocks that need to be turned on. That means,
> > if you turn off any of the three, it won't boot anymore.
> 
> For my tests, I didn't fully boot the kernel but inserted a while(1) after
> the clock init sequence. I had the wachdog already initialized in the
> bootloader, so after a few seconds it would boot again - or not.
> 
> If you fully boot the kernel, then the driver will probably switch on
> the UART1 clock, so you don't notice the effect anymore. But the kernel
> can hang _before_ drivers come up, and it should still work. That's
> what hardware watchdogs are for.
> 
> As a sidenote, it should be clear that this patch is a workaround for
> a serious chip bug of the MX35.