From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 15 Nov 2021 20:55:11 +0200 From: Ilias Apalodimas Subject: Re: [PATCH net-next v6] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA Message-ID: References: <20211013091920.1106-1-linyunsheng@huawei.com> <1090744a-3de6-1dc2-5efe-b7caae45223a@huawei.com> <644e10ca-87b8-b553-db96-984c0b2c6da1@collabora.com> <93173400-1d37-09ed-57ef-931550b5a582@huawei.com> <8c688448-e8a9-5a6b-7b17-ccd294a416d3@redhat.com> MIME-Version: 1.0 In-Reply-To: <8c688448-e8a9-5a6b-7b17-ccd294a416d3@redhat.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline List-ID: To: Jesper Dangaard Brouer Cc: Yunsheng Lin , brouer@redhat.com, Guillaume Tucker , davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@openeuler.org, hawk@kernel.org, akpm@linux-foundation.org, peterz@infradead.org, will@kernel.org, jhubbard@nvidia.com, yuzhao@google.com, mcroce@microsoft.com, fenghua.yu@intel.com, feng.tang@intel.com, jgg@ziepe.ca, aarcange@redhat.com, guro@fb.com, "kernelci@groups.io" [...] > > > > > > > > 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) It shouldn't be that hard. However when we removed that we were hoping we had no active consumers. So we'll have to fix this and check for other 32-bit boards with LPAE and page_pool handling the DMA mappings. But the point now is that this is far from a 'hardware configuration' of 32-bit CPU + 64-bit DMA. Every armv7 and x86 board can get that. So I was thinking it's better to revert this and live with the 'weird' handling in the code. Cheers /Ilias