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Message-ID: <5509A500.7020109@nokia.com>
Date:   Wed, 18 Mar 2015 17:17:04 +0100
From:   Alexander Sverdlin <alexander.sverdlin@nokia.com>
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To:     ext David Daney <ddaney@caviumnetworks.com>
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>,
        Rob Herring <robh@kernel.org>, Jiri Kosina <jkosina@suse.cz>,
        Randy Dunlap <rdunlap@infradead.org>,
        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
References: <55097811.8050003@nokia.com> <5509A39C.6010707@caviumnetworks.com>
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Hello David,

On 18/03/15 17:11, ext David Daney 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>
> 
> Can you say how it was tested.  In principle I have no objections, but it would be nice to know how it was validated.

What do you want to know, how we've debugged IRQ latency and found the root cause or how we figured out
that delay is not necessary? I'm pretty sure that there is HW which requires it. Maybe it's even Octeon itself...
But putting udelay() in this callbacks is wrong wrong wrong. 

-- 
Best regards,
Alexander Sverdlin.