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Date: Wed, 18 Nov 2015 18:56:56 -0800 From: Ray Jui <rjui@...adcom.com> To: Marc Zyngier <marc.zyngier@....com> CC: Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>, Hauke Mehrtens <hauke@...ke-m.de>, <linux-kernel@...r.kernel.org>, <bcm-kernel-feedback-list@...adcom.com>, <linux-pci@...r.kernel.org> Subject: Re: [PATCH 4/5] PCI: iproc: Add iProc PCIe MSI support Hi Marc, On 11/18/2015 5:37 PM, Ray Jui wrote: > Hi Marc, > > On 11/18/2015 12:48 AM, Marc Zyngier wrote: >> On Tue, 17 Nov 2015 16:31:54 -0800 >> Ray Jui <rjui@...adcom.com> wrote: >>> +static int iproc_msi_irq_domain_alloc(struct irq_domain *domain, >>> + unsigned int virq, unsigned int nr_irqs, >>> + void *args) >>> +{ >>> + struct iproc_msi *msi = domain->host_data; >>> + int i, msi_irq; >>> + >>> + mutex_lock(&msi->bitmap_lock); >>> + >>> + for (i = 0; i < nr_irqs; i++) { >>> + msi_irq = find_first_zero_bit(msi->used, msi->nirqs); >> >> This is slightly puzzling. Do you really have at most 6 MSIs? Usually, >> we end up with a larger number of MSIs (32 or 64) multiplexed on top of >> a small number of wired interrupts. Here, you seem to have a 1-1 >> mapping. Is that really the case? > > Yes, based on the poorly written iProc PCIe arch doc, :), we seem to > have 1-1 mapping between each wired interrupt and MSI, with each MSI > handled by an event queue, that consists of 64x word entries allocated > from host memory (DDR). The MSI data is stored in the low 16-bit of each > entry, whereas the upper 16-bit of each entry is reserved for the iProc > PCIe controller for its own use. > In fact, let me confirm with our ASIC team on the above statement. The iProc PCIe arch doc is in fact not very clear on this.... >> >> If so (and assuming the wired interrupts are always contiguous), you >> shouldn't represent this as a chained interrupt (a multiplexer), but as >> a stacked irqchip, similar to what GICv2m does. >> > > Okay, I think I might be missing something here, but I thought I > currently have a stacked irqdomain (chip), i.e., GIC -> inner_domain -> > MSI domain? > > And does this imply I should expect 'nr_irqs' in this routine to be > always zero and therefore I can get rid of the for loop here (same in > the domain free routine)? > Thanks, Ray -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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