Messages in this thread Patch in this message | | | Date | Thu, 25 Aug 2022 21:59:24 +0100 | Subject | Re: [PATCH v5 2/2] PCI: dwc: Add support for 64-bit MSI target address | From | Robin Murphy <> |
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On 2022-08-25 19:50, Will McVicker wrote: > Since not all devices require a 32-bit MSI address, add support to the > PCIe host driver to allow setting the DMA mask to 64-bits if the 32-bit > allocation fails. This allows kernels to disable ZONE_DMA32 and bounce > buffering (swiotlb) without risking not being able to get a 32-bit address > during DMA allocation. > > Basically, in the slim chance that there are no 32-bit allocations > available, the current PCIe host driver will fail to allocate the msi_msg > page due to a DMA address overflow (seen in [1]). With this patch, the > PCIe host can retry the allocation with a 64-bit DMA mask if the current > PCIe device advertises 64-bit support via its MSI capabilities. > > [1] https://lore.kernel.org/all/Yo0soniFborDl7+C@google.com/ > > Reported-by: kernel test robot <lkp@intel.com> > Signed-off-by: Will McVicker <willmcvicker@google.com> > Reviewed-by: Rob Herring <robh@kernel.org> > Acked-by: Jingoo Han <jingoohan1@gmail.com> > --- > .../pci/controller/dwc/pcie-designware-host.c | 38 ++++++++++++++----- > drivers/pci/controller/dwc/pcie-designware.c | 8 ++++ > drivers/pci/controller/dwc/pcie-designware.h | 1 + > 3 files changed, 38 insertions(+), 9 deletions(-) > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c > index 39f3b37d4033..8928a9a29d58 100644 > --- a/drivers/pci/controller/dwc/pcie-designware-host.c > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c > @@ -330,6 +330,9 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp) > u64 *msi_vaddr; > int ret; > u32 ctrl, num_ctrls; > + bool msi_64bit = false; > + bool retry_64bit = false; > + u16 msi_capabilities; > > for (ctrl = 0; ctrl < MAX_MSI_CTRLS; ctrl++) > pp->irq_mask[ctrl] = ~0; > @@ -367,16 +370,33 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp) > dw_chained_msi_isr, pp); > } > > - ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32)); > - 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"); > + msi_capabilities = dw_pcie_msi_capabilities(pci); > + if (msi_capabilities & PCI_MSI_FLAGS_ENABLE) > + msi_64bit = msi_capabilities & PCI_MSI_FLAGS_64BIT; > > - msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data, > - GFP_KERNEL); > - if (!msi_vaddr) { > - dev_err(dev, "Failed to alloc and map MSI data\n"); > - dw_pcie_free_msi(pp); > - return -ENOMEM; > + while (true) { > + dev_dbg(dev, "Setting MSI DMA mask to %s-bit.\n", > + retry_64bit ? "64" : "32");
If only we has some sort of "variable" that could could store a numerical value, think of the possibilities... :)
> + ret = dma_set_mask_and_coherent(dev, retry_64bit ? > + DMA_BIT_MASK(64) : > + DMA_BIT_MASK(32)); > + if (ret) > + dev_warn(dev, "Failed to set DMA mask to %s-bit.\n", > + retry_64bit ? "64" : "32");
Setting a 64-bit mask should never fail, since it represents having no possible limitation whatsoever (I'm not sure if there are any platforms left where setting a 32-bit mask can actually fail in practice either, but I have no strong opinion on the fate of the existing warning).
> + > + msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data, > + GFP_KERNEL); > + if (!msi_vaddr) { > + dev_err(dev, "Failed to alloc and map MSI data\n");
Possibly a mattrer of personal taste, but I'd say try to avoid dev_err() for things that aren't actually fatal; if you're still able to continue on, at best it's a warning, not an error. Especially if your use-case *expects* the 32-bit allocation fail. There's nothing more offputting than booting a typical vendor kernel and watching it scream tons of errors that look EXTREMELY IMPORTANT yet are also apparently inconsequential.
> + if (msi_64bit && !retry_64bit) { > + retry_64bit = true; > + continue; > + } > + > + dw_pcie_free_msi(pp); > + return -ENOMEM; > + } > + break;
TBH the whole loop design is a bit baroque for me, I'd have gone for a more straightforward tweak to the existing flow, something like:
msi_vaddr = NULL; ret = dma_set_mask(32); if (!ret) msi_vaddr = dma_alloc(); if (!msi_vaddr && msi_64bit) { dev_warn(); dma_set_mask(64); msi_vaddr = dma_alloc(); } if (!msi_vaddr) { dev_err(); return; } However I'm happy that you've captured the important functional point, so I'll leave the style matters up to Lorenzo.
Thanks, Robin.
> } > > return 0; > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c > index c6725c519a47..650a7f22f9d0 100644 > --- a/drivers/pci/controller/dwc/pcie-designware.c > +++ b/drivers/pci/controller/dwc/pcie-designware.c > @@ -82,6 +82,14 @@ u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap) > } > EXPORT_SYMBOL_GPL(dw_pcie_find_capability); > > +u16 dw_pcie_msi_capabilities(struct dw_pcie *pci) > +{ > + u8 offset; > + > + offset = dw_pcie_find_capability(pci, PCI_CAP_ID_MSI); > + return dw_pcie_readw_dbi(pci, offset + PCI_MSI_FLAGS); > +} > + > static u16 dw_pcie_find_next_ext_capability(struct dw_pcie *pci, u16 start, > u8 cap) > { > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h > index a871ae7eb59e..45fcdfc8c035 100644 > --- a/drivers/pci/controller/dwc/pcie-designware.h > +++ b/drivers/pci/controller/dwc/pcie-designware.h > @@ -332,6 +332,7 @@ void dw_pcie_version_detect(struct dw_pcie *pci); > > u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap); > u16 dw_pcie_find_ext_capability(struct dw_pcie *pci, u8 cap); > +u16 dw_pcie_msi_capabilities(struct dw_pcie *pci); > > int dw_pcie_read(void __iomem *addr, int size, u32 *val); > int dw_pcie_write(void __iomem *addr, int size, u32 val);
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