From: Bjorn Helgaas <helgaas@kernel.org>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: rubini@gnudd.com, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, hch@infradead.com, linux-kernel@vger.kernel.org,
linux-pci@vger.kernel.org
Subject: Re: [PATCH] x86/PCI: sta2x11: use default DMA address translation ops
Date: Thu, 17 Oct 2019 17:41:20 -0500 [thread overview]
Message-ID: <20191017224120.GA68948@google.com> (raw)
In-Reply-To: <20191016165138.24636-1-nsaenzjulienne@suse.de>
Hi Nicolas,
I'm hoping Christoph will chime in and one of the x86 guys will merge
this, since I'm not a DMA expert. Trivial comments/questions below.
On Wed, Oct 16, 2019 at 06:51:37PM +0200, Nicolas Saenz Julienne wrote:
> The devices found behind this PCIe chip have unusual DMA mapping
> constraints as there is an AMBA interconnect placed in between them and
> the different PCI endpoints. The offset between physical memory
> addresses and AMBA's view is provided by reading a PCI config register,
> which is saved and used whenever DMA mapping is needed.
>
> It turns out that this DMA setup can be represented by properly setting
> 'dma_pfn_offset', 'dma_bus_mask' and 'dma_mask' during the PCI device
> enable fixup. And ultimately allows us to get rid of this device's
> custom DMA functions.
>
> Aside from the code deletion and DMA setup, sta2x11_pdev_to_mapping() is
> moved to avoid warnings whenever CONFIG_PM is not enabled.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> - pci_read_config_dword(pdev, AHB_BASE(0), &map->amba_base);
> +
> + pci_read_config_dword(pdev, AHB_BASE(0), &amba_base);
> + dev->dma_pfn_offset = PFN_DOWN(-amba_base);
> + dev->bus_dma_mask = amba_base + STA2X11_AMBA_SIZE - 1;
I think of a mask as typically being one less than a power of two, but
that's not the case here, e.g., STA2X11_AMBA_SIZE - 1 == 0x1fffffff
(512MB-1), so if amba_size is 1G, the mask will be 0x5fffffff.
Just double-checking to be sure that's what you intend.
> + pci_set_consistent_dma_mask(pdev, amba_base + STA2X11_AMBA_SIZE - 1);
> + pci_set_dma_mask(pdev, amba_base + STA2X11_AMBA_SIZE - 1);
Maybe add a local variable instead of repeating the "amba_base + ..."
expression three times?
> /* Configure AHB mapping */
> pci_write_config_dword(pdev, AHB_PEXLBASE(0), 0);
> @@ -252,14 +156,25 @@ static void sta2x11_map_ep(struct pci_dev *pdev)
> pci_write_config_dword(pdev, AHB_CRW(i), 0);
>
> dev_info(&pdev->dev,
> - "sta2x11: Map EP %i: AMBA address %#8x-%#8x\n",
> - sta2x11_pdev_to_ep(pdev), map->amba_base,
> - map->amba_base + STA2X11_AMBA_SIZE - 1);
> + "sta2x11: Map EP %i: AMBA address %#8x-%#8llx\n",
> + sta2x11_pdev_to_ep(pdev), amba_base, dev->bus_dma_mask);
This would read better as
amba_base, amba_base + STA2X11_AMBA_SIZE - 1
I know that's the same dev->bus_dma_mask, but a "mask" is not the
obvious name for the end of a range.
next prev parent reply other threads:[~2019-10-17 22:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 16:51 [PATCH] x86/PCI: sta2x11: use default DMA address translation ops Nicolas Saenz Julienne
2019-10-17 22:41 ` Bjorn Helgaas [this message]
2019-10-18 8:51 ` Nicolas Saenz Julienne
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