linux-kernel - Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support

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Date:	Mon, 5 Oct 2015 08:56:28 +0100
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Vlad Zolotarov <vladz@...udius-systems.com>
Cc:	linux-kernel@...r.kernel.org, mst@...hat.com, hjk@...sjkoch.de,
	corbet@....net, bruce.richardson@...el.com,
	avi@...udius-systems.com, gleb@...udius-systems.com,
	stephen@...workplumber.org, alexander.duyck@...il.com
Subject: Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support

On Mon, Oct 05, 2015 at 10:41:39AM +0300, Vlad Zolotarov wrote:
> >>+struct msix_info {
> >>+	int num_irqs;
> >>+	struct msix_entry *table;
> >>+	struct uio_msix_irq_ctx {
> >>+		struct eventfd_ctx *trigger;	/* MSI-x vector to eventfd */
> >Why are you using eventfd for msi vectors?  What's the reason for
> >needing this?
> 
> A small correction - for MSI-X vectors. There may be only one MSI vector per
> PCI function and if it's used it would use the same interface as a legacy
> INT#x interrupt uses at the moment.
> So, for MSI-X case the reason is that there may be (in most cases there will
> be) more than one interrupt vector. Thus, as I've explained in a PATCH1
> thread we need a way to indicated each of them separately. eventfd seems
> like a good way of doing so. If u have better ideas, pls., share.

You need to document what you are doing here, I don't see any
explaination for using eventfd at all.

And no, I don't know of any other solution as I don't know what you are
trying to do here (hint, the changelog didn't document it...)

> >You haven't documented how this api works at all, you are going to have
> >to a lot more work to justify this, as this greatly increases the
> >complexity of the user/kernel api in unknown ways.
> 
> I actually do documented it a bit. Pls., check PATCH3 out.

That provided no information at all about how to use the api.

If it did, you would see that your api is broken for 32/64bit kernels
and will fall over into nasty pieces the first time you try to use it
there, which means it hasn't been tested at all :(

thanks,

greg k-h
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