linux-kernel - Re: crypto/cavium MSI-X fixups

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Date:   Wed, 22 Feb 2017 08:27:52 +0100
From:   Christoph Hellwig <hch@....de>
To:     David Daney <ddaney@...iumnetworks.com>
Cc:     Christoph Hellwig <hch@....de>,
        George Cherian <gcherian@...iumnetworks.com>,
        George Cherian <george.cherian@...ium.com>,
        David Daney <david.daney@...ium.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: crypto/cavium MSI-X fixups

On Tue, Feb 21, 2017 at 09:36:04AM -0800, David Daney wrote:
> With respect to pci_enable_msix(), what do you recommend as a replacement?  

pci_alloc_irq_vectors.  In fact I have a tree ready for after -rc1
that removes pci_enable_msix() entirely.

> For the crypto/cavium driver, you recommend pci_alloc_irq_vectors(), which 
> works well if the required MSI-X indexes are contiguous starting at zero.   
> What would be used for a device that has 184 MSI-X, but only a sparse 
> subset (fewer than half) of these are required for the driver operation.  
> It would waste system resources to use an API that forces us to allocate 
> 184 when only 80 are required.

Currently we don't have a good API for that.  I've not been through all
users of pci_enable_msix_{range,exact} yet, but so far I've only found
one user not using all vectors from 0 to some limit.  Depending how many
such users we have and how they'll look I will have to look into an API
to support that use case.