On 01/18/2017 07:15 PM, Brian Masney wrote:
On Fri, Jan 13, 2017 at 10:21:15AM -0700, Stephen Warren wrote:
On 01/13/2017 04:48 AM, Brian Masney wrote:
On Thu, Jan 12, 2017 at 11:47:48AM -0700, Stephen Warren wrote:
On 01/12/2017 11:32 AM, Brian Masney wrote:
On Thu, Jan 12, 2017 at 11:02:14AM -0700, Stephen Warren wrote:
On 01/12/2017 01:57 AM, Brian Masney wrote:
The bcm2835 driver polls the monitor and selects the highest resolution
that is available. This patch allows optionally setting the video-mode
environment variable so that a different video resolution can be used.
If the environment variable is not specified, then it will fall back to
using the old behavior of using the maximum allowable resolution.

This patch is needed to fix an issue booting an upstream Linux kernel
on a Raspberry Pi 2 with a Pi Top screen. Previously, the bcm2835 would
select the 1366x768 resolution (which is a supported resolution),
however the screen would be unreadable. (See
https://www.flickr.com/photos/masneyb/30942037416/ for picture). Using
this patch, the resolution 1024x768 can be selected and is readable on
the screen.

Doesn't this mean that the RPi firmware is reporting the wrong resolution?
If so, isn't the correct fix to get an updated firmware that reports the
correct resolution, rather than patching each piece of SW to ignore the
FW-reported resolution? Or, if this is caused by incorrect EDID in the Pi
Top, then fix the EDID EEPROM on that.

Perhaps there are other use-cases for using a non-default resolution, but to
support that, you'd need to make a call into the FW to request and configure
that non-default resolution, not just ignore what resolution the FW

Hi Stephen,
   The Pi Top screen works correctly with the 1366x768 resolution when
booting the 4.4 kernel provided by the Raspberry Pi foundation in
stock Raspbian (no u-boot). (There are no outside provided drivers from
Pi Top.) When booting with u-boot, I can't use the 1366x768 resolution,
even when setting the resolution manually using my patch. When auto
detection is in place, u-boot correctly detects the 1366x768 resolution
according to debugging messages that I see on the serial console.
1024x768 is the highest resolution that I can get a working display with
the Pi Top and u-boot. I also tried changing the display depth.

   I tried booting u-boot using the latest Raspberry Pi firmware and the
older firmware provided with the Raspbian 4.4 kernel. In both cases, the
screen correctly displays the rainbow square at the top left when the
GPU is booting, but then the screen becomes garbled when it gets to
u-boot and the bcm2835 code sets the resolution.

   I tried going through the Pi Top vendor for help but didn't get very
far with them. I'm open to other suggestions to try.

Is the bad image that you get static/fixed, or does it move about randomly?

If it's static/fixed, I wonder if the issue is with the memory pitch
calculation. What value does bcm2835_pitch have without your patch? (and
with your patch, I think it's uninitialized?).

I wonder if you round the value of bcm2835_pitch up to a multiple of 256 (or
something like that), then perhaps the issue may be solved? If you change
the pitch value, and you notice the angle of the diagonal edges in the image
change, the issue is almost certainly related to this pitch value.

I can't recall how the mainline kernel driver works now. If it also uses the
property mailbox to configure the display, and you're just using the dumb
simplefb driver, perhaps you can compare the memory layout parameters the
kernel uses when it's working to what U-Boot uses when it's not working.

The image is fixed. I can see when the Linux Kernel boots and the
console messages scroll across the screen.

Without my patch, u-boot detects the screen resolution as 1366x768 with
a pitch of 5504. With my patch, 1024x768 uses a pitch of 2048.

I reverted my u-boot patch and tried hard coding the pitch to the values
5376, 5632, 2048, 4096, and 6144 with no success. Once I read what the
pitch value does, I also tried 5464 (1366 x 4 (for 32bpp)) and 2732.

Is this related?

(See "I think I've just fixed that")

(See the diff in the BCMVideo file)

Another thing to try might be to remove the SET_* operations from U-Boot's
property mailbox calls (I think the FW always initializes video out anyway,
so U-Boot doesn't need to set anything up), and simply invoke the relevant
GET_* operations to query where the buffer is and its size. IIRC I didn't do
that because you can only query certain information as a side-effect of
asking the FW to allocate a frame-buffer though (i.e. the info comes back in
a SET_xxx/ALLOCATE_xxx response message, but there's no GET_xxx to query the
data without modifying the configuration or re-allocating anything).

I attached a patch (uboot-bcm2835-release-fb.patch) that releases the frame
buffer before the other mailbox properties are set. This did not fix my display

Hmm. That's a pity.

I also tried removing all of the SET_ operations
(uboot-bcm2835-remote-mbox-sets.patch). The screen stays on the rainbow
screen when the GPU is initialized. I can see through the serial console
that the pi boots normally.

Applying both patches gives a blank screen so it appears that releasing
the frame buffer works.

In the BCMVideo diff that you referenced, there are two rows between
ARM2VC_Tag_FBRelease and ARM2VC_Tag_End with zeros:

+tagrel  DCD     tagrellen
+        DCD     0

Those two should be this in U-Boot:

/* All message buffers must start with this header */
struct bcm2835_mbox_hdr {
        u32 buf_size;
        u32 code;

+        DCD     ARM2VC_Tag_FBRelease
+        DCD     0
+        DCD     0

Those three should be this in U-Boot:

 * A message buffer contains a list of tags. Each tag must also start with
 * a standardized header.
struct bcm2835_mbox_tag_hdr {
        u32 tag;
        u32 val_buf_size;
        u32 val_len;

+        DCD     ARM2VC_Tag_End
+tagrellen *     . - tagrel

Are these parameters? I don't see places to put those in

I also forgot to mention in my last email that changing the value of
bcm2835_pitch does not cause the output to move.

Oh. That's odd. I'd suggest asking about this on the Raspberry Pi forums, or perhaps on github as a bug/question in the Raspberry Pi firmware repository. There's nothing U-Boot-specific about all this; U-Boot is just sending in standard messages that the RPi firmware understands.
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