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<p>Hi all,</p>
<p>I'm struggling to solve a problem which in theory should be quite
straight forward. This email is a bit of a brain dump so apologies
for being all over the place.<br>
</p>
<p>I'm working on an embedded device where u-boot displays a logo
which I want the kernel to preserve. However I find the display
gets blanked as soon as the kernel starts executing.</p>
<p>As I understand it, the first step is to get the kernel to
reserve the frame-buffer memory (and hand it to the FB driver
later on). So I added the following device tree entry:</p>
<p><tt> reserved-memory {</tt><tt><br>
</tt><tt> #address-cells = <1>;</tt><tt><br>
</tt><tt> #size-cells = <1>;</tt><tt><br>
</tt><tt> ranges;</tt><tt><br>
</tt><tt><br>
</tt><tt> display_reserved: fb@0 {</tt><tt><br>
</tt><tt> no-map;</tt><tt><br>
</tt><tt> reg = <0x3ffa5000
0x0005b000>;</tt><tt><br>
</tt><tt> };</tt><tt><br>
</tt><tt> };</tt><tt><br>
</tt><br>
</p>
<p>The memory area reflects the FB memory allocated by u-boot.</p>
<p>This is an atmel SAMA5D2 based board with 512M RAM in the
0x20000000-0x40000000 range.<br>
</p>
However, I find the display is blanked even before the FB driver
starts.
<p>I have confirmed that the device tree entry is processed by
placing printks in drivers/of/of_reserved_mem.c
(<a class="moz-txt-link-freetext" href="http://elixir.free-electrons.com/linux/latest/source/drivers/of/of_reserved_mem.c#L85">http://elixir.free-electrons.com/linux/latest/source/drivers/of/of_reserved_mem.c#L85</a>).</p>
<p>I also added the following line at the same spot to see if that
area is at least accessible:</p>
<p>*(unsigned int*)<tt>0x3ffa5000 </tt> = 0xffffffff</p>
<p>And I observed the following result:</p>
<ol>
<li>The kernel hangs</li>
<li>The display is not yet blanked at this point</li>
</ol>
<p>Writing to the same location from within the u-boot shell places
a white pixel on the display.</p>
<p>Could anyone suggest what areas I need to look at to solve this
problem? Any tips and suggestions will be greatly appreciated.</p>
<p>Thank you</p>
<p>Dushara<br>
</p>
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