linux-kernel - Re: [PATCH v4 0/8] Allwinner H6 Mali GPU support

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Date:   Thu, 16 May 2019 14:21:35 +0100
From:   Steven Price <steven.price@....com>
To:     Robin Murphy <robin.murphy@....com>,
        Rob Herring <rob.e.herring@...il.com>,
        Clément Péron <peron.clem@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        David Airlie <airlied@...ux.ie>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 0/8] Allwinner H6 Mali GPU support

On 16/05/2019 12:19, Robin Murphy wrote:
[...]
> I was expecting to see a similar behaviour to my T620 (which I now
> assume was down to 64-bit job descriptors sort-of-but-not-quite working)
> but this does look a bit more fundamental - the fact that it's a level 1
> fault with VA == head == tail suggests to me that the MMU can't see the
> page tables at all to translate anything. I really hope that the H6 GPU
> integration doesn't suffer from the same DMA offset as the Allwinner
> display pipeline stuff, because that would be a real pain to support in
> io-pgtable.

Assuming you mean the case where the physical address (as seen by the
CPU) is different from the dma address (as seen by the GPU), then I
highly doubt it because mali_kbase doesn't support it:

[from kbase_mem_pool_alloc_page() in mali_kbase_mem_pool.c]:

	dma_addr = dma_map_page(dev, p, 0, PAGE_SIZE, DMA_BIDIRECTIONAL);
	if (dma_mapping_error(dev, dma_addr)) {
		__free_page(p);
		return NULL;
	}

	WARN_ON(dma_addr != page_to_phys(p));


That being said it's quite possible there could be something in the bus
which needs configuring to make this work - in which case your best bet
is to look at the vendor kernel and see if anything extra is poked when
the Mali driver is loaded.

Steve