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Subject: Re: [PATCH] dma-pool: Do not allocate pool memory from CMA
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Amit Pundir <amit.pundir@linaro.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        David Rientjes <rientjes@google.com>,
        linux-rpi-kernel@lists.infradead.org, jeremy.linton@arm.com,
        iommu@lists.linux-foundation.org,
        lkml <linux-kernel@vger.kernel.org>,
        John Stultz <john.stultz@linaro.org>,
        Sumit Semwal <sumit.semwal@linaro.org>
Date:   Tue, 21 Jul 2020 18:27:24 +0200
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On Tue, 2020-07-21 at 20:52 +0530, Amit Pundir wrote:

[...]

> > > > 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;
> };

Pretty standard, and similar to what it's being used upstream by
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.

Let's get a bigger hammer, I'm just looking for clues here. Can you
apply this and provide the dmesg output.

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 6bc74a2d5127..2160676bf488 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -268,6 +268,8 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
                        schedule_work(&atomic_pool_work);
        }
 
+       dev_info(dev, "%s: size %lx, phys addr %llx, flags 0x%x\n", __func__, size, phys, flags);
+
        return ptr;
 }
  

Regards,
Nicolas