Re: [PATCH] PCI: dwc: ep: Do not map more memory than needed to raise a MSI/MSI-X IRQ

["Krzysztof Wilczyński" <kw@linux.com>]

Hello,

> > In dw_pcie_ep_init() we allocate memory from the EPC address space that we
> > will later use to raise a MSI/MSI-X IRQ. This memory is only freed in
> > dw_pcie_ep_deinit().
> > 
> > Performing this allocation in dw_pcie_ep_init() is to ensure that we will
> > not fail to allocate memory from the EPC address space when trying to raise
> > a MSI/MSI-X IRQ.
> > 
> > We still map/unmap this memory every time we raise an IRQ, in order to not
> > constantly occupy an iATU, especially for controllers with few iATUs.
> > (So we can still fail to raise an MSI/MSI-X IRQ if all iATUs are occupied.)
> > 
> > When allocating this memory in dw_pcie_ep_init(), we allocate
> > epc->mem->window.page_size memory, which is the smallest unit that we can
> > allocate from the EPC address space.
> > 
> > However, when writing/sending the msg data, which is only 2 bytes for MSI,
> > 4 bytes for MSI-X, in either case a single writel() is sufficient. Thus,
> > the size that we need to map is a single PCI DWORD (4 bytes).
> > 
> > This is the size that we should send in to the pci_epc_ops::align_addr()
> > API. It is align_addr()'s responsibility to return a size that is aligned
> > to the EPC page size, for platforms that need a special alignment.
> > 
> > Modify the align_addr() call to send in the proper size that we need to
> > map.
> > 
> > Before this patch on a system with a EPC page size 64k, we would
> > incorrectly map 128k (which is larger than our allocation) instead of 64k.
> > 
> > After this patch, we will correctly map 64k (a single page). (We should
> > never need to map more than a page to write a single DWORD.)
> > 
> > Fixes: f68da9a67173 ("PCI: dwc: ep: Use align addr function for dw_pcie_ep_raise_{msi,msix}_irq()")
> > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> 
> FWIW,
> 
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Picked this tag, too.  Thank you!

	Krzysztof