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From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Cc: Andrew Murray <andrew.murray@arm.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Masami Hiramatsu <masami.hiramatsu@linaro.org>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Kishon Vijay Abraham I <kishon@ti.com>
Subject: Re: [PATCH 2/2] PCI: uniphier: Add checking whether PERST# is deasserted
Date: Thu, 21 Nov 2019 16:47:05 +0000
Message-ID: <20191121164705.GA14229@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <20191108163026.0DFB.4A936039@socionext.com>

On Fri, Nov 08, 2019 at 04:30:27PM +0900, Kunihiko Hayashi wrote:
> > However, If I understand correctly, doesn't your solution only work some
> > of the time? What happens if you boot both machines at the same time,
> > and PERST# isn't asserted prior to the kernel booting?
> 
> I think it contains an annoying problem.
> 
> If PERST# isn't toggled prior to the kernel booting, PERST# remains asserted
> and the RC driver can't access PCI bus.
> 
> As a result, this patch works and deasserts PERST# (and EP configuration will
> be lost). So boot sequence needs to include deasserting PERST#.

I am sorry but I have lost you. Can you explain to us why checking
that PERST# is deasserted guarantees you that:

- The EP has bootstrapped
- It is safe not to toggle it again (and also skip
  uniphier_pcie_ltssm_enable())

Please provide details of the HW configuration so that we understand
what's actually supposed to happen and why this patch fixes the
issue you are facing.

Thanks,
Lorenzo

  parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-07  4:58 [PATCH 1/2] PCI: uniphier: Set mode register to host mode Kunihiko Hayashi
2019-11-07  4:58 ` [PATCH 2/2] PCI: uniphier: Add checking whether PERST# is deasserted Kunihiko Hayashi
2019-11-07 10:02   ` Andrew Murray
2019-11-07 11:52     ` Kunihiko Hayashi
2019-11-07 12:46       ` Andrew Murray
2019-11-08  7:30         ` Kunihiko Hayashi
2019-11-08  9:59           ` Andrew Murray
2019-11-21 16:47           ` Lorenzo Pieralisi [this message]
2019-11-22 11:53             ` Kunihiko Hayashi
2019-12-04 10:05               ` Kunihiko Hayashi
2019-12-06  6:58                 ` Kishon Vijay Abraham I
2019-12-06  8:58                   ` Kunihiko Hayashi
2019-12-06  9:01                     ` Kishon Vijay Abraham I
2019-12-09  2:35                       ` Kunihiko Hayashi
2019-11-07  9:52 ` [PATCH 1/2] PCI: uniphier: Set mode register to host mode Andrew Murray
2019-11-21 16:49 ` Lorenzo Pieralisi

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