Re: [PATCH v5 4/7] PCI: endpoint: pci-epf-vntb: Export endpoint DMA channels

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] pci-epf-vntb: Build failure due to non-constant expression in offsetof()
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commit d7f27f0fe4a25aa5e8eb677eb623fec735ae8a53
Author: Koichiro Den <den@valinux.co.jp>

PCI: endpoint: pci-epf-vntb: Export endpoint DMA channels

An RC may use endpoint-local DMA read channels to transfer data directly
to an endpoint DMA address once both sides agree to use them. This commit
reserves read channels, describes the controller, adds a dma_bar configfs
attribute, and maps resources through the selected dma_bar.

Link: https://lore.kernel.org/r/3tgny5jkxjw3foqgkohlgmw4lh4trv63swgdc3kvi7qxzpf222@avh4tiacqn2a/

> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
[ ... ]
> +static int epf_ntb_dw_edma_collect(struct epf_ntb *ntb,
> +				   struct epf_ntb_dma *dma,
> +				   const struct pci_epc_aux_resource *ctrl,
> +				   const struct pci_epc_aux_resource *resources,
> +				   unsigned int count)
> +{
[ ... ]
> +	dma->ctrl.magic = EPF_NTB_DMA_MAGIC;
> +	dma->ctrl.revision = EPF_NTB_DMA_REVISION;
> +	dma->ctrl.type = EPF_NTB_DMA_TYPE_DW_EDMA;
> +	dma->ctrl.submap.bar = barno;
> +	dma->ctrl.length = offsetof(struct epf_ntb_dma_ctrl,
> +				    chan[dma->rd_ch_cnt]);

[Severity: Low]
Will this cause a build failure on Clang? The code uses a runtime variable
(dma->rd_ch_cnt) as an array index inside the offsetof macro. 

While GCC may tolerate this as an extension, Clang strictly rejects 
non-constant indices in __builtin_offsetof, which is what the kernel's 
offsetof relies on. Could this size be calculated manually using struct_size 
or a similar approach instead?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261009045949.1109871-1-den@valinux.co.jp?part=4