How to set DMA coherent pool size on the Pogoplug E02

[ErnieW]

I've got a pink E02 Pogoplug which I use as a PVR running TVHeadend plugged in to a DVB-T stick and a USB DVB-S receiver. I had it working fine with a Tevii S660 satellite box, but that died, and the replacement I bought, a Technisat SkyStar USB HD (bought because other people described it as needing no fiddling to set up) fails while loading the driver with the message

ERROR: 256 KiB atomic DMA coherent pool is too small!
Please increase it with coherent_pool= kernel parameter!

There's an old thread in the archives http://archlinuxarm.org/forum/viewtopic.php?f=23&t=6185 where someone carefully lists all the steps they went through which ended up in a bricked box, but it's not so clear on how to do it the right way. I assume I need to use fw_setenv rather thatn blparm, but I've tried a couple of options which are sitting there when I do a fw_printenv but have no effect when I reboot (I suppose a follow up question is how to delete wrong entries) .

fw_setenv coherent_pool 1M doesn't work, but shows as coherent_pool=1M and adding it to the alarm_args string is equally ineffective.

I'm currently running 3.14.2-1-ARCH #1 PREEMPT Sun Apr 27 02:18:07 MDT 2014 armv5tel GNU/Linux and updated uboot sometime back to enable newer kernels, although I'm not sure exactly which version I've got.

Thanks in advance for any suggestions.

[pepedog]

Try adding a conf file, eg /etc/sysctl.d/99-mycustom.conf, and add there
https://wiki.archlinux.org/index.php/Sysctl
I'm not going to tell you how, but it should be fw_setenv bootargs alltheexistingbootargs coherent_pool 1M
Get this wrong and you are in trouble. If sysctl works, all the better

[ErnieW]

No joy there, I'm afraid, but interestingly a Pacman -Syu gives the message "replace uboot-env with alarm/uboot-tools" so that might work. Time to go swot up on another undocumented package.

[ErnieW]

OK, for anyone else trying to sort this one out, the answer was to upgrade to the new uBoot (make sure you're on Linux-kirkwood first - read the wiki https://github.com/archlinuxarm/u-boot/wiki and check the other threads from people who had problems. It worked straight away for me). Then create the /boot/uEnv.txt file (I used nano) and tweak the optargs variable until you find a value that doesn't throw up an error in dmesg. 1M wasn't enough, but 4M worked fine.

$this->bbcode_second_pass_code('', 'pacman -S uboot-pogo_e02

nano /boot/uEnv.txt

optargs=coherent_pool=4M')