Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <17c2cba5-fcb3-1e02-b488-65f4dafe6367@linux.intel.com>
Date:   Fri, 2 Sep 2022 16:57:32 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Firefox/91.0 Thunderbird/91.11.0
Subject: Re: [PATCH v2 1/3] PCI/PTM: Preserve PTM Root Select
Content-Language: en-US
To:     Bjorn Helgaas <helgaas@kernel.org>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Rajvi Jingar <rajvi.jingar@linux.intel.com>,
        "Rafael J . Wysocki" <rafael@kernel.org>
Cc:     Koba Ko <koba.ko@canonical.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        "David E . Box" <david.e.box@linux.intel.com>,
        linux-pci@vger.kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>
References: <20220902233543.390890-1-helgaas@kernel.org>
 <20220902233543.390890-2-helgaas@kernel.org>
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
In-Reply-To: <20220902233543.390890-2-helgaas@kernel.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi,

On 9/2/22 4:35 PM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> When disabling PTM, there's no need to clear the Root Select bit.  We
> disable PTM during suspend, and we want to re-enable it during resume.
> Clearing Root Select here makes re-enabling more complicated.
> 
> Per PCIe r6.0, sec 7.9.15.3, "When set, if the PTM Enable bit is also Set,
> this Time Source is the PTM Root," so if PTM Enable is cleared, the value
> of Root Select should be irrelevant.
> 
> Preserve Root Select to simplify re-enabling PTM.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> Cc: David E. Box <david.e.box@linux.intel.com>
> ---

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>  drivers/pci/pcie/ptm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
> index 368a254e3124..b6a417247ce3 100644
> --- a/drivers/pci/pcie/ptm.c
> +++ b/drivers/pci/pcie/ptm.c
> @@ -42,7 +42,7 @@ void pci_disable_ptm(struct pci_dev *dev)
>  		return;
>  
>  	pci_read_config_word(dev, ptm + PCI_PTM_CTRL, &ctrl);
> -	ctrl &= ~(PCI_PTM_CTRL_ENABLE | PCI_PTM_CTRL_ROOT);
> +	ctrl &= ~PCI_PTM_CTRL_ENABLE;
>  	pci_write_config_word(dev, ptm + PCI_PTM_CTRL, ctrl);
>  }
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer