Hello.
I compiled the following code as the device tree source.
/dts-v1/;
/plugin/;
/* Reserve 256kB DDR memory for the ping/pong buffers */
/ {
fragment@0 {
target = <&ocp>;
__overlay__ {
reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
pruadc_reserved: pruadc_reserved@0x90000000 {
reg = <0x90000000 0x00040000>;
no-map;
status = "okay";
};
};
};
};
};
But after booting, there is no trace of the reserved memory in the
/proc/iomem file (there is no gap in "System RAM"). I also tested a large
number of different sources, but none of them came up with a result.
Can you share here the device tree source that you have used?
On Sunday, December 2, 2018 at 11:57:55 PM UTC+3:30, Ken Shirriff wrote:
>
> Thanks for the replies, Charles. I figured out the problem. The dts
> <https://git.ti.com/apps/tida01555/blobs/master/dts/am335x-boneblack-pruadc.dts>
>
> I was using tried to reserve 256K at 0x9ffc0000. However, system RAM ends
> at 9fdfffff, which is earlier, so the reservation never showed up in the
> RAM numbers. (I'm unclear what's in that last 2 meg of RAM, and if it's
> okay to reserve part of it.)
>
> I changed the range to start at 0x90000000 and now it shows up as a change
> when running "free". As well, the reserved memory hole is nicely visible in
> /proc/iomem:
> # grep RAM /proc/iomem
> 80000000-8fffffff : System RAM
> 90040000-9fdfffff : System RAM
>
> So I think everything is working with memory reservation now.
>
> Ken
>
> On Sunday, December 2, 2018 at 10:59:09 AM UTC-8, Charles Steinkuehler
> wrote:
>>
>> On 12/2/2018 12:22 PM, Ken Shirriff wrote:
>> >
>> > I also tried increasing the amount of reserved memory from 256K to 4M
>> and
>> > didn't see any change. I increased the size way beyond physical memory,
>> and
>> > didn't get any errors. So I suspect it is being ignored. Do I need a
>> kernel
>> > flag or something to reserve memory?
>>
>> No.
>>
>> > So, is there any way to verify that the memory is getting reserved? (I
>> > suspect nothing is reserved, so I would be writing to random memory if
>> I
>> > tried to use the buffer.)
>>
>> Other than noticing the reduced amount of free ram, I don't think the
>> reserved memory regions show up until/unless they are requested by a
>> kernel driver.
>>
>> > Ken
>> >
>> > [1]: I got the reserved-memory to load two ways. I figured out that I
>> need
>> > to use target-path = "/"; in the dtc file so it gets loaded under the
>> root
>> > node. Next, in case reserved-memory didn't work as an overlay, I edited
>> > am335x-bone-common.dtsi under /opt/source/dtb-4.14-ti.
>>
>> There's likely an issue in your device tree. Make sure your entries
>> are showing up under /sys:
>>
>> $ find /sys/firmware/devicetree/base/reserved-memory/ -type f
>> /sys/firmware/devicetree/base/reserved-memory/ranges
>> /sys/firmware/devicetree/base/reserved-memory/#address-cells
>> /sys/firmware/devicetree/base/reserved-memory/#size-cells
>> /sys/firmware/devicetree/base/reserved-memory/NewTek_Reserved/reg
>> /sys/firmware/devicetree/base/reserved-memory/NewTek_Reserved/name
>> /sys/firmware/devicetree/base/reserved-memory/NewTek_Video/reg
>> /sys/firmware/devicetree/base/reserved-memory/NewTek_Video/name
>> /sys/firmware/devicetree/base/reserved-memory/name
>>
>> ~$ hd /sys/firmware/devicetree/base/reserved-memory/NewTek_Reserved/reg
>> 00000000 18 00 00 00 08 00 00 00 |........|
>> 00000008
>>
>> NOTES:
>> * This is from a Zynq (not a BBB), but it should match if you're using
>> a recent 4.x kernel.
>>
>> * The names should match whatever you have in device-tree
>>
>> * The values in the "reg" file are in wacky device-tree byte order,
>> the hex dump above corresponds to a "reg = <0x18000000 0x08000000>;"
>> entry in the device-tree.
>>
>> * You don't need the status="okay"; entries in your node
>>
>> * Don't use overlays and put the reserved-memory node at the root of
>> the device-tree (I think you already figured this out).
>>
>> * Double (and then triple) check for typos!
>>
>> * Note that just because something shows up in the "live" device tree
>> (under /sys/firmware/devicetree/base/) doesn't mean the kernel did
>> anything with it. If you misspell "reserved-memory" for instance,
>> your node will show up in the device tree, but you won't have actually
>> reserved any memory. The kernel doesn't complain about unknown or
>> unexpected elements in the device-tree.
>>
>> --
>> Charles Steinkuehler
>> [email protected]
>>
>
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