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Date:   Thu, 21 Nov 2019 16:47:05 +0000
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
Message-ID: <20191121164705.GA14229@e121166-lin.cambridge.arm.com>
References: <20191107205239.65C1.4A936039@socionext.com>
 <20191107124617.GA43905@e119886-lin.cambridge.arm.com>
 <20191108163026.0DFB.4A936039@socionext.com>
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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