From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Warren <swarren@nvidia.com>
Date: Mon, 24 Nov 2014 21:21:24 -0700
Subject: [U-Boot] Raspberry Pi with driver model
In-Reply-To: <CAPnjgZ3s5Kc__nFX+6F_tb_378_MrSsyxj0gUKYUpwYzA=sHPg@mail.gmail.com>
References: <CAPnjgZ3s5Kc__nFX+6F_tb_378_MrSsyxj0gUKYUpwYzA=sHPg@mail.gmail.com>
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On 11/24/2014 08:58 AM, Simon Glass wrote:
> Hi Stephen,
> 
> There was another thread where you reported a hang when booting
> Raspberry Pi with driver model. It can be repeated by applying this
> patch and trying to boot with syslinux.
> 
> http://patchwork.ozlabs.org/patch/392180/
> 
> When it hangs, the HDMI display displays lots of spaces, then lots of
> dots, scrolling forever. The serial console displays nothing further.
> 
> I narrowed the problem down to writing to address 0. So it is easy to
> repeat with something like 'mw 0 0'.
> 
> However I'm really not sure what is going on. Something with driver
> model seems to make address 0 sensitive to writes. I can't see what
> that might be, but I don't understand the platform very well. Do you
> have any ideas?

The problem seems to be that inside pl01x_serial_probe() (well, I assume
all serial functions), dev_get_priv() returns 0, which ends up using
address 0 as the UART address since that's the first field in struct
pl01x_priv.

I found this by amending pl01x_serial_probe() as follows, and dumping
the data after boot:

uint32_t *log = (uint32_t *)(128*1024*1024);
uint32_t log_i = 1;

static int pl01x_serial_probe(struct udevice *dev)
{
	struct pl01x_serial_platdata *plat = dev_get_platdata(dev);
	struct pl01x_priv *priv = dev_get_priv(dev);

        log[log_i++] = (uint32_t)dev;
        log[log_i++] = (uint32_t)plat;
        log[log_i++] = (uint32_t)priv;
        log[0] = log_i;
	priv->regs = (struct pl01x_regs *)plat->base;
	priv->type = plat->type;
	return pl01x_generic_serial_init(priv->regs, priv->type);
}

U-Boot> md.l 0x08000000
08000000: 00000007 07fffaf8 0003972c 00000000    ........,.......
08000010: 1db4e108 1df8372c 00000000 00000000    ....,7..........

It seems a bit odd that pl01x_serial_probe() is called twice, but
perhaps that's expected?