Re: [PATCH net-next v6] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

[Jesper Dangaard Brouer]

On 15/11/2021 13.21, Yunsheng Lin wrote:
> On 2021/11/15 20:10, Ilias Apalodimas wrote:
> > On Mon, 15 Nov 2021 at 13:53, Ilias Apalodimas
> > <ilias.apalodimas@xxxxxxxxxx> wrote:
> > > On Mon, Nov 15, 2021 at 11:34:59AM +0800, Yunsheng Lin wrote:
> > > > On 2021/11/12 17:21, Guillaume Tucker wrote:
> > > > > On 09/11/2021 12:02, Yunsheng Lin wrote:
> > > > > > On 2021/11/9 17:58, Guillaume Tucker wrote:
> > > > > > > Hi Yunsheng,
> > > > > > >
> > > > > > > Please see the bisection report below about a boot failure on
> > > > > > > rk3288-rock2-square which is pointing to this patch.  The issue
> > > > > > > appears to only happen with CONFIG_ARM_LPAE=y.
> > > > > > >
> > > > > > > Reports aren't automatically sent to the public while we're
> > > > > > > trialing new bisection features on kernelci.org but this one
> > > > > > > looks valid.
> > > > > > >
> > > > > > > Some more details can be found here:
> > > > > > >
> > > > > > >    https://linux.kernelci.org/test/case/id/6189968c3ec0a3c06e3358fe/
> > > > > > >
> > > > > > > Here's the same revision on the same platform booting fine with a
> > > > > > > plain multi_v7_defconfig build:
> > > > > > >
> > > > > > >    https://linux.kernelci.org/test/plan/id/61899d322c0e9fee7e3358ec/
> > > > > > >
> > > > > > > Please let us know if you need any help debugging this issue or
> > > > > > > if you have a fix to try.
> > > > > >
> > > > > > The patch below is removing the dma mapping support in page pool
> > > > > > for 32 bit systems with 64 bit dma address, so it seems there
> > > > > > is indeed a a drvier using the the page pool with PP_FLAG_DMA_MAP
> > > > > > flags set in a 32 bit systems with 64 bit dma address.
> > > > > >
> > > > > > It seems we might need to revert the below patch or implement the
> > > > > > DMA-mapping tracking support in the driver as mentioned in the below
> > > > > > commit log.
> > > > > >
> > > > > > which ethernet driver do you use in your system?
> > > > >
> > > > > Thanks for taking a look and sorry for the slow reply.  Here's a
> > > > > booting test job with LPAE disabled:
> > > > >
> > > > >      https://linux.kernelci.org/test/plan/id/618dbb81c60c4d94503358f1/
> > > > >      https://storage.kernelci.org/mainline/master/v5.15-12452-g5833291ab6de/arm/multi_v7_defconfig/gcc-10/lab-collabora/baseline-nfs-rk3288-rock2-square.html#L812
> > > > >
> > > > > [    8.314523] rk_gmac-dwmac ff290000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
> > > > >
> > > > > So the driver is drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c
> > > >
> > > > Thanks for the report, this patch seems to cause problem for 32-bit
> > > > system with LPAE enabled.
> > > >
> > > > As LPAE seems like a common feature for 32 bits system, this patch
> > > > might need to be reverted.
> > > >
> > > > @Jesper, @Ilias, what do you think?
> > >
> > >
> > > So enabling LPAE also enables CONFIG_ARCH_DMA_ADDR_T_64BIT on that board?
> > > Doing a quick grep only selects that for XEN.  I am ok reverting that,  but
> > > I think we need to understand how the dma address ended up being 64bit.
> >
> > So looking a bit closer, indeed enabling LPAE always enables this.  So
> > we need to revert the patch.
> > Yunsheng will you send that?
>
> Sure.

Why don't we change that driver[1] to not use page_pool_get_dma_addr() ?

 [1] drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c

I took a closer look and it seems the driver have struct 
stmmac_rx_buffer in which is stored the dma_addr it gets from 
page_pool_get_dma_addr().

See func: stmmac_init_rx_buffers

 static int stmmac_init_rx_buffers(struct stmmac_priv *priv,
				struct dma_desc *p,
				int i, gfp_t flags, u32 queue)
 {

	if (!buf->page) {
		buf->page = page_pool_dev_alloc_pages(rx_q->page_pool);
		if (!buf->page)
			return -ENOMEM;
		buf->page_offset = stmmac_rx_offset(priv);
	}
	[...]

	buf->addr = page_pool_get_dma_addr(buf->page) + buf->page_offset;

	stmmac_set_desc_addr(priv, p, buf->addr);
	[...]
 }

I question if this driver really to use page_pool for storing the 
dma_addr as it just extract it and store it outside page_pool?

@Ilias it looks like you added part of the page_pool support in this 
driver, so I hope you can give a qualified guess on:
How much work will it be to let driver do the DMA-map itself?
(and not depend on the DMA-map feature provided by page_pool)

--Jesper