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Message-ID: <20220928114136.4yvtfnrcril3jkgg@mobilestation>
Date: Wed, 28 Sep 2022 14:41:36 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Will McVicker <willmcvicker@...gle.com>
Cc: Serge Semin <fancer.lancer@...il.com>,
Jingoo Han <jingoohan1@...il.com>,
Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Rob Herring <robh@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>,
Bjorn Helgaas <bhelgaas@...gle.com>, kernel-team@...roid.com,
Vidya Sagar <vidyas@...dia.com>,
Christoph Hellwig <hch@...radead.org>,
Robin Murphy <robin.murphy@....com>, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org,
"Isaac J . Manjarres" <isaacmanjarres@...gle.com>
Subject: Re: [PATCH v5 1/2] PCI: dwc: Drop dependency on ZONE_DMA32
On Thu, Aug 25, 2022 at 06:50:24PM +0000, Will McVicker wrote:
> Re-work the msi_msg DMA allocation logic to use dmam_alloc_coherent() which
> uses the coherent DMA mask to try to return an allocation within the DMA
> mask limits. With that, we now can drop the msi_page parameter in struct
> dw_pcie_rp. This allows kernel configurations that disable ZONE_DMA32 to
> continue supporting a 32-bit DMA mask. Without this patch, the PCIe host
> device will fail to probe when ZONE_DMA32 is disabled.
As Rob already said here
https://lore.kernel.org/all/CAL_JsqJh=d-B51b6yPBRq0tOwbChN=AFPr-a19U1QdQZAE7c1A@mail.gmail.com/
and I mentioned in this thread
https://lore.kernel.org/linux-pci/20220912000211.ct6asuhhmnatje5e@mobilestation/
DW PCIe MSI doesn't cause any DMA due to the way the iMSI-RX engine is
designed. So reserving any real system memory is a waste of one in
this case. Reserving DMA-coherent even more inappropriate since it
can be expensive on some platforms (see note in Part Ia of
Documentation/core-api/dma-api.rst). For instance on MIPS32 with
non-corehent common DMA.
>
> Fixes: 35797e672ff0 ("PCI: dwc: Fix MSI msi_msg DMA mapping")
> Reported-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
> Signed-off-by: Will McVicker <willmcvicker@...gle.com>
> Acked-by: Jingoo Han <jingoohan1@...il.com>
> Reviewed-by: Rob Herring <robh@...nel.org>
> ---
> .../pci/controller/dwc/pcie-designware-host.c | 28 +++++--------------
> drivers/pci/controller/dwc/pcie-designware.h | 1 -
> 2 files changed, 7 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 7746f94a715f..39f3b37d4033 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -267,15 +267,6 @@ static void dw_pcie_free_msi(struct dw_pcie_rp *pp)
>
> irq_domain_remove(pp->msi_domain);
> irq_domain_remove(pp->irq_domain);
> -
> - if (pp->msi_data) {
> - struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> - struct device *dev = pci->dev;
> -
> - dma_unmap_page(dev, pp->msi_data, PAGE_SIZE, DMA_FROM_DEVICE);
> - if (pp->msi_page)
> - __free_page(pp->msi_page);
> - }
> }
>
> static void dw_pcie_msi_init(struct dw_pcie_rp *pp)
> @@ -336,6 +327,7 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
> struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> struct device *dev = pci->dev;
> struct platform_device *pdev = to_platform_device(dev);
> + u64 *msi_vaddr;
> int ret;
> u32 ctrl, num_ctrls;
>
> @@ -375,22 +367,16 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
> dw_chained_msi_isr, pp);
> }
>
> - ret = dma_set_mask(dev, DMA_BIT_MASK(32));
> + ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
This has been redundant in the first place since none of the DW PCIe
low-level drivers update the mask, and it's of 32-bits wide by default
anyway:
https://elixir.bootlin.com/linux/latest/source/drivers/of/platform.c#L167
> if (ret)
> dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n");
>
> - pp->msi_page = alloc_page(GFP_DMA32);
> - pp->msi_data = dma_map_page(dev, pp->msi_page, 0,
> - PAGE_SIZE, DMA_FROM_DEVICE);
> - ret = dma_mapping_error(dev, pp->msi_data);
> - if (ret) {
> - dev_err(pci->dev, "Failed to map MSI data\n");
> - __free_page(pp->msi_page);
> - pp->msi_page = NULL;
> - pp->msi_data = 0;
> + msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
> + GFP_KERNEL);
Changing the whole device DMA-mask due to something that doesn't
perform seems inappropriate. I'd suggest to preserve the ZONE_DMA32
here until there is something like suggested by @Robin
https://lore.kernel.org/linux-pci/1e63a581-14ae-b4b5-a5bf-ca8f09c33af6@arm.com/
in the last paragraph is implemented. Especially seeing there still
common drivers in kernel which still rely on that zone.
-Sergey
> + if (!msi_vaddr) {
> + dev_err(dev, "Failed to alloc and map MSI data\n");
> dw_pcie_free_msi(pp);
> -
> - return ret;
> + return -ENOMEM;
> }
>
> return 0;
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 09b887093a84..a871ae7eb59e 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -243,7 +243,6 @@ struct dw_pcie_rp {
> struct irq_domain *irq_domain;
> struct irq_domain *msi_domain;
> dma_addr_t msi_data;
> - struct page *msi_page;
> struct irq_chip *msi_irq_chip;
> u32 num_vectors;
> u32 irq_mask[MAX_MSI_CTRLS];
> --
> 2.37.2.672.g94769d06f0-goog
>
>
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