Re: [PATCH 1/2] OF/PCI: Export inbound memory interface to PCI RC drivers.

From: Marek Vasut <marek.vasut@gmail.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci@vger.kernel.org, Oza Pawandeep <oza.oza@broadcom.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Simon Horman <horms+renesas@verge.net.au>,
	Wolfram Sang <wsa@the-dreams.de>,
	linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH 1/2] OF/PCI: Export inbound memory interface to PCI RC drivers.
Date: Mon, 30 Sep 2019 23:46:18 +0200	[thread overview]
Message-ID: <bfe084be-48ee-3005-e9e1-7fe03d4f406c@gmail.com> (raw)
In-Reply-To: <20190930214046.GA201622@google.com>

On 9/30/19 11:40 PM, Bjorn Helgaas wrote:
> This would follow the convention for subject lines:
> 
>   PCI: OF: Add of_pci_get_dma_ranges() for inbound DMA restrictions
> 
> On Fri, Aug 09, 2019 at 07:34:48PM +0200 wrote:
>> From: Oza Pawandeep
>>
>> The patch exports interface to PCIe RC drivers so that,
>> Drivers can get their inbound memory configuration.
> 
> IIUC this interface (of_pci_get_dma_ranges()) is not used directly by
> *drivers*; it is used by of_bus_pci_get_dma_ranges() in the next
> patch, and it's called by the driver core via this path:
> 
>   really_probe
>     pci_dma_configure                     # pci_bus_type.dma_configure
>       of_dma_configure
> 	of_dma_get_range
> 	  bus->get_dma_ranges
> 	    of_bus_pci_get_dma_ranges     # of_busses[0].get_dma_ranges
> 	      of_pci_get_dma_ranges
> 
>> It provides basis for IOVA reservations for inbound memory
>> holes, if RC is not capable of addressing all the host memory,
>> Specifically when IOMMU is enabled and on ARMv8 where 64bit IOVA
>> could be allocated.
>>
>> It handles multiple inbound windows, and returns resources,
>> and is left to the caller, how it wants to use them.
> 
> This should say exactly what the problem is, maybe even with a link to
> a problem report.  I assume it is something like "RC <X> cannot
> address all of host memory, and if we happen to allocate a buffer
> that's not addressable, DMA to the buffer fails".  It'd be nice to
> know what the failure looks like (SERR# asserted, panic, reboot, etc).

[...]

While it's good that someone finally looked at these patches, these were
since superseded by the following series:
https://patchwork.ozlabs.org/cover/1168166/

-- 
Best regards,
Marek Vasut