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From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Marek Behún" <marek.behun@nic.cz>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Tomasz Maciej Nowak" <tmn505@gmail.com>,
	Xogium <contact@xogium.me>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Fri, 10 Jul 2020 10:18:00 +0100	[thread overview]
Message-ID: <20200710091800.GA3419@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <20200709150959.wq6zfkcy4m6hvvpl@pali>

On Thu, Jul 09, 2020 at 05:09:59PM +0200, Pali Rohár wrote:

[...]

> > I understand that but the bridge bus resource can be trimmed to just
> > contain the root bus because that's the only one where there is a
> > chance you can enumerate a device.
> 
> It is possible to register only root bridge without endpoint?

It is possible to register the root bridge with a trimmed IORESOURCE_BUS
so that you don't enumerate anything other than the root port.

> > I would like to get Bjorn's opinion on this, I don't like these "link is
> > up" checks in config accessors (they are racy and honestly it is a
> > run-time check that does not make much sense, either it is always
> > true/false or it is inevitably racy)
> 
> It is runtime check, but does not have to be always true/false. I have
> tested more Compex wifi cards and under certain conditions they
> "disappear" from the bus during usage.

I would be very grateful if you could describe what happens in HW
when these conditions trigger - I would like to understand if this
issue is aardvark specific or it isn't.

> So I think it still make sense to do this "fast" check as it is only
> optimization.

I will merge this patch but I'd also like to understand the underlying
issue better.

Thanks,
Lorenzo

WARNING: multiple messages have this Message-ID
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Tomasz Maciej Nowak" <tmn505@gmail.com>,
	linux-pci@vger.kernel.org, Xogium <contact@xogium.me>,
	linux-kernel@vger.kernel.org, "Marek Behún" <marek.behun@nic.cz>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	linux-arm-kernel@lists.infradead.org,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>
Subject: Re: [PATCH v3] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Fri, 10 Jul 2020 10:18:00 +0100	[thread overview]
Message-ID: <20200710091800.GA3419@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <20200709150959.wq6zfkcy4m6hvvpl@pali>

On Thu, Jul 09, 2020 at 05:09:59PM +0200, Pali Rohár wrote:

[...]

> > I understand that but the bridge bus resource can be trimmed to just
> > contain the root bus because that's the only one where there is a
> > chance you can enumerate a device.
> 
> It is possible to register only root bridge without endpoint?

It is possible to register the root bridge with a trimmed IORESOURCE_BUS
so that you don't enumerate anything other than the root port.

> > I would like to get Bjorn's opinion on this, I don't like these "link is
> > up" checks in config accessors (they are racy and honestly it is a
> > run-time check that does not make much sense, either it is always
> > true/false or it is inevitably racy)
> 
> It is runtime check, but does not have to be always true/false. I have
> tested more Compex wifi cards and under certain conditions they
> "disappear" from the bus during usage.

I would be very grateful if you could describe what happens in HW
when these conditions trigger - I would like to understand if this
issue is aardvark specific or it isn't.

> So I think it still make sense to do this "fast" check as it is only
> optimization.

I will merge this patch but I'd also like to understand the underlying
issue better.

Thanks,
Lorenzo

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-07-10  9:18 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 14:31 [PATCH] " Pali Rohár
2020-05-28 14:31 ` Pali Rohár
2020-05-28 16:26 ` Bjorn Helgaas
2020-05-28 16:26   ` Bjorn Helgaas
2020-05-28 16:38   ` Pali Rohár
2020-05-28 16:38     ` Pali Rohár
2020-05-28 16:49     ` Bjorn Helgaas
2020-05-28 16:49       ` Bjorn Helgaas
2020-05-29  8:30       ` Pali Rohár
2020-05-29  8:30         ` Pali Rohár
2020-06-30 12:31         ` Pali Rohár
2020-06-30 12:31           ` Pali Rohár
2020-06-30 13:51     ` Bjorn Helgaas
2020-06-30 13:51       ` Bjorn Helgaas
2020-06-30 14:04       ` Pali Rohár
2020-06-30 14:04         ` Pali Rohár
2020-06-30 14:58         ` Bjorn Helgaas
2020-06-30 14:58           ` Bjorn Helgaas
2020-07-01  8:08           ` Pali Rohár
2020-07-01  8:08             ` Pali Rohár
2020-07-01  8:20 ` [PATCH v2] " Pali Rohár
2020-07-01  8:20   ` Pali Rohár
2020-07-01 21:34   ` Bjorn Helgaas
2020-07-01 21:34     ` Bjorn Helgaas
2020-07-02  8:23     ` Pali Rohár
2020-07-02  8:23       ` Pali Rohár
2020-07-02  8:30 ` [PATCH v3] " Pali Rohár
2020-07-02  8:30   ` Pali Rohár
2020-07-09 11:35   ` Lorenzo Pieralisi
2020-07-09 11:35     ` Lorenzo Pieralisi
2020-07-09 12:22     ` Pali Rohár
2020-07-09 12:22       ` Pali Rohár
2020-07-09 14:47       ` Lorenzo Pieralisi
2020-07-09 14:47         ` Lorenzo Pieralisi
2020-07-09 15:09         ` Pali Rohár
2020-07-09 15:09           ` Pali Rohár
2020-07-10  9:18           ` Lorenzo Pieralisi [this message]
2020-07-10  9:18             ` Lorenzo Pieralisi
2020-07-10 15:44             ` Pali Rohár
2020-07-10 15:44               ` Pali Rohár
2020-07-10 16:08               ` Bjorn Helgaas
2020-07-10 16:08                 ` Bjorn Helgaas
2020-07-10 19:30                 ` Pali Rohár
2020-07-10 19:30                   ` Pali Rohár
2020-07-10 20:08                   ` Bjorn Helgaas
2020-07-10 20:08                     ` Bjorn Helgaas
2020-07-13  8:27             ` Pali Rohár
2020-07-13  8:27               ` Pali Rohár
2020-07-13 11:23               ` Lorenzo Pieralisi
2020-07-13 11:23                 ` Lorenzo Pieralisi
2020-07-13 14:50                 ` Pali Rohár
2020-07-13 14:50                   ` Pali Rohár
2020-07-13 16:41                   ` Lorenzo Pieralisi
2020-07-13 16:41                     ` Lorenzo Pieralisi
2020-07-14  7:38                     ` Pali Rohár
2020-07-14  7:38                       ` Pali Rohár
2020-07-15 12:17                 ` Pali Rohár
2020-07-15 12:17                   ` Pali Rohár
2020-07-15 16:21                   ` Lorenzo Pieralisi
2020-07-15 16:21                     ` Lorenzo Pieralisi
2020-07-21  8:57                     ` Pali Rohár
2020-07-21  8:57                       ` Pali Rohár
2020-07-21 10:48                       ` Lorenzo Pieralisi
2020-07-21 10:48                         ` Lorenzo Pieralisi

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