Hi,
On 10 January 2015 at 03:50, Ian Campbell ijc@hellion.org.uk wrote:
On Fri, 2015-01-09 at 13:13 +0200, Siarhei Siamashka wrote:
If yes then I think it is confusing to modify this comment, and the comment before the pre-console #defines should mention that the buffer is boottime only/short lived etc.
Just in case if something goes really wrong (in theory it shouldn't, but in practice you know...) it is still somewhat safer to keep the buffer in its own dedicated area and keep everything else out.
Nothing in those defines is protecting anything though, if the kernel is more than 15M it will still overwrite that area.
Perhaps a better place for the pre-console buffer would be right before the framebuffer (or at the top of RAM if no video on the board), with modifications to bootm_size or not depending on the answer to the original question above.
If this needs any kind of runtime address calculations instead of compile time constants, then IMHO it becomes unnecessarily complicated.
One for Hans I think, my understanding was that the framebuffer was at the top of RAM, but having bootm_size set to 0xf0000000 unconditionally doesn't match that. I suppose the idea is that it corresponds with the smallest board because it's not worth making it dynamic (I think I recall Hans saying something like that at the time).
I think you could safely put the early buffer at 0xf000000-DELTA (and adjust bootm_size to match), rather than worrying about packing it up below the real framebuffer.
Anyway. The sunxi part of these changes just needs to assign some memory area to the pre-console buffer. In the end it does not really matter which one. The size also does not need to be too large. For example 1920 * 1080 / (8 * 16) = 16200. It means that only ~16K of the log buffer can fully cover the FullHD display using the 8x16 font. And this is even assuming no line breaks. I picked 1M only because it was the smallest unit of the address space allocation in sunxi-common.h :-)
I don't think it needs to be allocated in 1M chunks, it just happens to have been arbitrarily chosen that way so far.
If you want to keep the early buffer down in that region then I think it'd be better to steal a few KB from the end of the fdt, script or pxe (all of which will never be anywhere near 1MB) than stealing 1M off the end of the kernel (it's not totally inconceivable that a kernel might be approaching ~15M in size)
I don't think it is a good idea to use the 'pre-console buffer' after the console exists. It is a misnomer.
Also, the reason that the pre-console buffer has pre-allocated memory is to work around the lack of memory allocation before relocation. Now that we have initf_mallloc() called very early in boot we could consider allocating the space instead.
I think this patch is a good feature to implement, but I agree with others that hard-coded memory locations for U-Boot features should not exist except in exceptional circumstances (e.g. very early boot).
Re passing the U-Boot console to the kernel, see as an example the cbmem_console.c driver. It only works on x86 at present and only with coreboot. It works as a stdio driver, so skips the first part of U-Boot's output.
So I suggest:
1. Remove the pre-console address and just have a size. Allocate the space after initf_malloc(). Store the details (buffer start, size and current pointer) in global_data 2. Add a general mechanism to record the console into a buffer by renaming and adjusting the existing code. It can then be set up pre-console, post-console but pre-stdio, and then post-stdio for recording what is passed to Linux.
Regards, Simon