linux-kernel - Re: [PATCH v6 02/10] PCI: imx6: Fix i.MX8MP PCIe EP's occasional failure to trigger MSI

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Message-ID: <20240706173954.GB3980@thinkpad>
Date: Sat, 6 Jul 2024 23:09:54 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Frank Li <Frank.li@....com>
Cc: Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	NXP Linux Team <linux-imx@....com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pci@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	devicetree@...r.kernel.org, Jason Liu <jason.hui.liu@....com>
Subject: Re: [PATCH v6 02/10] PCI: imx6: Fix i.MX8MP PCIe EP's occasional
 failure to trigger MSI

On Mon, Jul 01, 2024 at 02:32:59PM -0400, Frank Li wrote:
> On Sat, Jun 29, 2024 at 06:35:25PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Jun 17, 2024 at 04:16:38PM -0400, Frank Li wrote:
> > > From: Richard Zhu <hongxing.zhu@....com>
> > > 
> > > Correct occasional MSI triggering failures in i.MX8MP PCIe EP by apply 64KB
> > > hardware alignment requirement.
> > > 
> > > MSI triggering fail if the outbound MSI memory region (ep->msi_mem) is not
> > > aligned to 64KB.
> > > 
> > > In dw_pcie_ep_init():
> > > 
> > > ep->msi_mem = pci_epc_mem_alloc_addr(epc, &ep->msi_mem_phys,
> > > 				     epc->mem->window.page_size);
> > > 
> > 
> > So this is an alignment restriction w.r.t iATU. In that case, we should be
> > passing 'pci_epc_features::align' instead?
> 
> pci_epc_features::align already set.
> 
> pci_epc_mem_alloc_addr(
> 	...
> 	align_size = ALIGN(size, mem->window.page_size);
> 	order = pci_epc_mem_get_order(mem, align_size);
> 	...
> }
> 
> but pci_epc_mem_alloc_addr() align to page_size, instead of
> pci_epc_features::align.
> 

'window.page_size' is set to what is passed as 'page_size' argument to
pci_epc_mem_init(). In this case, 'ep->page_size' is passed which corresponds to
size of pages that can be allocated within the memory window.

Default value of 'ep->page_size' is PAGE_SIZE which is most likely 4K. So if
your hardware cannot allocate 4K pages within the memory window, then it
doesn't support splitting this OB region into 4K pages.

But this has nothing to do with alignment AFAIU since epc_features::align is
used for IB memory. This 'page_size' argument was introduced for some TI SoC
that doesn't handle PAGE_SIZE splitting of OB memory window. Reference:

52c9285d4745 ("PCI: endpoint: Add support for configurable page size")

Can you check if your SoC also suffers from the same limitation? If so, then you
should modify the commit message to make it clear.

- Mani

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