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Message-ID: <55098872.9010605@nokia.com>
Date:   Wed, 18 Mar 2015 15:15:14 +0100
From:   Alexander Sverdlin <alexander.sverdlin@nokia.com>
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To:     ext Jiri Kosina <jkosina@suse.cz>
CC:     Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org,
        David Daney <ddaney@cavium.com>, ddaney.cavm@gmail.com,
        "ext Daney, David" <David.Daney@caviumnetworks.com>,
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        Masanari Iida <standby24x7@gmail.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Rulf, Mathias (Nokia - DE/Ulm)" <mathias.rulf@nokia.com>
Subject: Re: [PATCH] pci: octeon: Remove udelay() causing huge IRQ latency
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Hi!

On 18/03/15 14:11, ext Jiri Kosina wrote:
>> udelay() in PCI/PCIe read/write callbacks cause 30ms IRQ latency on Octeon
>> > platforms because these operations are called from PCI_OP_READ() and
>> > PCI_OP_WRITE() under raw_spin_lock_irqsave().
>> > 
>> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
> I have no idea about the octeon platform, but how do you deal with the 
> fact that is stated by the comment you are removing? I.e.
> 
> 	/* Some PCI cards require delays when accessing config space. */
> 
> Is that not the case any more for some reason? If not, it really needs to 
> be explained in the changelog.

This udelay() should not have made its way upstream, someone overseen it during
code review. This is simply not allowed to have delayed read/write in the current
Linux PCI subsystem. And maybe there is no place for it at all.

-- 
Best regards,
Alexander Sverdlin.