Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

Amit Pundir
2020-07-21T15:23:08Z

On Tue, 21 Jul 2020 at 18:15, Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> wrote:
>
> On Tue, 2020-07-21 at 17:45 +0530, Amit Pundir wrote:
> > On Tue, 21 Jul 2020 at 16:45, Nicolas Saenz Julienne
> > <nsaenzjulienne@suse.de> wrote:
> > > On Tue, 2020-07-21 at 14:24 +0530, Amit Pundir wrote:
> > > > On Tue, 21 Jul 2020 at 14:09, Nicolas Saenz Julienne
> > > > <nsaenzjulienne@suse.de> wrote:
> > > > > Hi Amit,
> > > > > > Hi Nicolas,
> > > > > >
> > > > > > I see a boot regression with this commit d9765e41d8e9 "dma-
> > > > > > pool:
> > > > > > Do not allocate pool memory from CMA" on my Xiaomi Poco F1
> > > > > > (Qcom sdm845) phone running v5.8-rc6. I can't boot past the
> > > > > > bootloader splash screen with this patch.
> > > > > >
> > > > > > Phone boots fine if I revert this patch. I carry only one out
> > > > > > of
> > > > > > tree
> > > > > > dts patch https://lkml.org/lkml/2020/6/25/52. And since this
> > > > > > is a
> > > > > > stock
> > > > > > phone, I don't have access to serial/dmesg logs until I boot
> > > > > > to
> > > > > > AOSP
> > > > > > (adb) shell.
> > > > > >
> > > > > > Any thoughts as to what might be going wrong here? I'd be
> > > > > > happy
> > > > > > to
> > > > > > help debug things. For what it's worth, I don't see this
> > > > > > regression
> > > > > > on
> > > > > > other two sdm845 devices (db845c and Pixel 3) I tested on.
> > > > >
> > > > > Can you provide a boot log (even if without my patch) and the
> > > > > device-
> > > > > tree files? It'd help a lot figuring things out.
> > > >
> > > > Thank you for the prompt reply Nicolas.
> > > >
> > > > Here is the boot log with the reverted patch
> > > > https://pastebin.ubuntu.com/p/BrhPf83nKF/
> > > >
> > > > Here is my phone's dts
> > > > https://github.com/pundiramit/linux/commit/2a394c199deeaf4c91e0e008e8fba2a72f494d8c
> > >
> > > I'm at loss at what could be failing here. Your device should be
> > > able
> > > to address the whole 8GB memory space, which AFAIK is the max
> > > available
> > > on that smartphone family. But maybe the device-tree is lying, who
> > > knows...
> >
> > If it helps, my phone has 6GB memory space.
> >
> > > Can you try booting *without* my patch and this in the kernel
> > > command
> > > line: "cma=16M@0x100000000-0x200000000".
> >
> > It doesn't boot with this added kernel command line.
>
>
> For the record, this placed the CMA in the [4GB, 8GB] address space
> instead of you setup's default: [3GB, 4GB]. All atomic pools fall in
> that memory area without my patch, which makes me think some of the
> devices on your board might not like higher addresses.
>

Thank you Nicolas for the details. Though we don't set the CMA
alloc-ranges explicitly in upstream sdm845 dts, but I dug around and
found that CMA alloc-ranges in the downstream kernel are indeed in
lower address space.
https://github.com/MiCode/Xiaomi_Kernel_OpenSource/blob/dipper-q-oss/arch/arm64/boot/dts/qcom/sdm845.dtsi#L662

/* global autoconfigured region for contiguous allocations */
linux,cma {
compatible = "shared-dma-pool";
alloc-ranges = <0 0x00000000 0 0xffffffff>;
reusable;
alignment = <0 0x400000>;
size = <0 0x2000000>;
linux,cma-default;
};

> What happens if you boot with my troublesome patch with this in your
> device tree? (insert it at the bottom of sdm845-beryllium.dts)
>
> &soc {
> dma-ranges = <0 0 0 0 0x1 0>;
> };
>

Device still doesn't boot up to adb shell.

Regards,
Amit Pundir

> Regards,
> Nicolas
>
> > Regards,
> > Amit Pundir
> >
> > > Regards,
> > > Nicolas
> > >
> > > And here is my kernel tree just in case
> > > > https://github.com/pundiramit/linux/commits/beryllium-mainline
> > > >
> > > > Regards,
> > > > Amit Pundir
> > > >
> > > >
> > > > > Regards,
> > > > > Nicolas
> > > > >
> > > > > > Regards,
> > > > > > Amit Pundir
> > > > > >
> > > > > > > Reported-by: Jeremy Linton <jeremy.linton@arm.com>
> > > > > > > Signed-off-by: Nicolas Saenz Julienne <
> > > > > > > nsaenzjulienne@suse.de>
> > > > > > > ---
> > > > > > >
> > > > > > > An more costly alternative would be adding an option to
> > > > > > > dma_alloc_from_contiguous() so it fails when the allocation
> > > > > > > doesn't
> > > > > > > fall
> > > > > > > in a specific zone.
> > > > > > >
> > > > > > > kernel/dma/pool.c | 11 ++---------