Hi Simon,
On Wed, Mar 21, 2012 at 10:33 AM, Simon Glass sjg@chromium.org wrote:
Hi Graeme,
On Tue, Mar 20, 2012 at 4:28 PM, Graeme Russ graeme.russ@gmail.com wrote:
Hi Stephen, Simon,
On Wed, Mar 21, 2012 at 8:17 AM, Stephen Warren swarren@wwwdotorg.org wrote:
On 03/20/2012 02:13 PM, Simon Glass wrote:
Hi Stephen,
On Tue, Mar 20, 2012 at 12:57 PM, Stephen Warren swarren@wwwdotorg.org wrote:
This works together with a kernel change that looks at the scratchpad register to determine which of the many UARTs it should use for early printing:
http://www.spinics.net/lists/arm-kernel/msg154633.html
Note that this configuration only affects the kernel's decompressor and earlyprintk code. Once the kernel is initialized far enough to parse the device tree, the console is initialized using information contained therein.
Base on work by Doug Anderson dianders@chromium.org, but significantly rewritten.
Signed-off-by: Stephen Warren swarren@wwwdotorg.org
For the pre-console panic stuff, the point is that there may well be one UART used for the console, but *we don't know which one it is!*.
That's where we disagree.
For each board, there is a single fixed UART that should be used for both pre-console panic and the "real" console later. This is fixed by the single static board design.
I agree - The board designer should specify a 'default' debug port which is used for all character output prior to the 'configured' console port being initialised.
We can provide that, but if it is wrong for the board we are using, then there will be no output. Stephen's original complaint was a brick if there is no valid device tree. We need this to work!
In the 'normal' boot case, the default console should never have any output sent to it (unless it also happens to be the 'configured' console port) as Both U-Boot and Linux will use a pre console buffer to buffer any output prior to the 'configured' console being available
So I think there is a clear evidence that the 'Board panic no console' and 'Specify debugging serial port at boot' are intrinsicly related - Both U-Boot and Linux should be dumping their 'pre-console' messages to the same port and this port should be specified by the hardware designer
So that being the case, there should be a single CONFIG_ option which both patches should be using
We cannot select the UART via CONFIG - remember that all of these boards have the same U-Boot binary. Please read that again :-) The device tree is the only thing that distinguishes them. All of the CONFIG options are identical for all boards.
But I don't get it - In your Seaboard patch, you only use UARTD so in this case we could CONFIG_ it?
And it's sounding like for other scenarios you are going to resign yourself to there not being a common UART so you will send the pre-console (panic) message to multiple UARTs - something that should be avoided at all costs...
I know we are dealing with a corner case abnormal situation here, but something does not smell right... Maybe I'm not understanding something obvious yet...
Regards,
Graeme