netdev - Re: [net-next 10/10] net/mlx5e: Add support for PCI relaxed ordering

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Message-ID: <20200710122113.GR23676@nvidia.com>
Date:   Fri, 10 Jul 2020 09:21:13 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Saeed Mahameed <saeedm@...lanox.com>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>,
        Aya Levin <ayal@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>,
        "alexander.h.duyck@...ux.intel.com" 
        <alexander.h.duyck@...ux.intel.com>,
        "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [net-next 10/10] net/mlx5e: Add support for PCI relaxed ordering

On Fri, Jul 10, 2020 at 02:18:02AM +0000, Saeed Mahameed wrote:

> Be careful though to load driver with RO on and then setpci RO off.. 
> not sure what the side effects are, unstable driver maybe ?

According to the PCI spec HW should stop doing RO immediately once the
config space bit is cleared.

In any event continuing to issue RO won't harm anything.

> And not sure what should be the procedure then ? reload driver ? FW
> will get a notification from PCI ? 

At worst you'd have to reload the driver - continuing to use RO if the
driver starts with RO off is seriously broken and probably won't work
with the quirks to disable RO on buggy platforms.

But as above, the RO config space bit should have immedaite effect on
the device and it should stop using RO. The device HW itself has to
enforce this to be spec compliant.

Jason