[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v1 09/14] xen/arm: Add cmdline boot option "pci=on"

  • To: Julien Grall <julien@xxxxxxx>, Rahul Singh <Rahul.Singh@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 20 Aug 2021 16:37:24 +0200
  • Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=suse.com; dmarc=pass action=none header.from=suse.com; dkim=pass header.d=suse.com; arc=none
  • Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=ij/gM9WxNVKA4jhCN/biYFt4Nn/KgPsxvohxiIRTXW8=; b=eQEQkSGEhd7l1KoN/1R3ygsv6/0g3hVhNGXJFbUtKrMdaPFR04INLkVOwgphhoT5sUOGXSD3+dbmgzjoTQJ1Ul19BoSTEJXzpuRxabAXgqiDYBw2wn7uMknHGyuFa3IBwzMN5KIht7tAvcgAZaIBoRfGm9nlxEoo25Kw+4ATeMNMjnxEOz/WKs/mXeaSNMkLInGi+3Hb/POjIpkz4oQIaIx/SqY9p+qmjVTn3pl2+b8RhhK0YUwq78LZiGBfwUBUjxyF/YaXehwUpSoIKWBn1sCKqxC7BO9VbYoISREGDwaS61CP9WKcRNpP0aF9urkUiZGMyWItpSCj+JbOqYJ4WQ==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=d4qqTh1TwBZ+LCPjLVasVdJ1+suLDdA0dK7rJWM9Z9FQNvQ0lHBnJwQ2eT8PlNbWEvna4yLceoM3EKBLGquE/P9bvmkfkxxWCiSn6i7Ogtlz9IYbt3FVwKj9rPjoGzuyy8tSQ9D3m1ocdKmAIiQZYLoseDpCOQSzWha4tMWwO3tikpRouRRdfOt8gcsHcFxR09sOe3pTV/bC+hGDNgfdl2K+eYqSAylXNKZEME7XpK5WUrbkRWl5NASLQDpHJhZfcsdCu7sihB7Ff+7f2erL0Tjwqk9U6ciPoprfQQCkm6IGS++PifxkjQoKp+AgHvWo3PGjc2ybO+f1ve6O1dg7+g==
  • Authentication-results: epam.com; dkim=none (message not signed) header.d=none;epam.com; dmarc=none action=none header.from=suse.com;
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
  • Delivery-date: Fri, 20 Aug 2021 14:37:34 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 20.08.2021 16:34, Julien Grall wrote:
> On 20/08/2021 13:19, Rahul Singh wrote:
>>> On 19 Aug 2021, at 1:31 pm, Julien Grall <julien@xxxxxxx> wrote:
>>> On 19/08/2021 13:02, Rahul Singh wrote:
>>>> Add cmdline boot option "pci=on" to enable/disable the PCI init during
>>>> boot.
>>> I read this as "PCI" will be either disabled/enabled for the platform. 
>>> Whereas, I think it will be used to decide whether Xen discover PCI and PCI 
>>> passthrough is supported or not.
>> Yes. I will modify the option to "pci-passthrough== <boolean>"
>>> Can you also clarify why a user would want to select "pci=off"?
>> As pci-passthrough support emulate the PCI devices for DOM0 also, I thought 
>> if someone want to
>> boot the DOM0 without emulating the PCI device in XEN and wants to have 
>> direct access to device.
> Dom0 will always have direct access to the PCI device. The only 
> difference is whether the access to the hostbridge and config space will 
> be trapped by Xen. I expect the both to mainly happen during boot and 
> therefore the overhead will be limited.
>> I am ok to drop this patch if you feel adding the option is not required at 
>> all.
> One of the reason I could see this option to be useful is to figure out 
> if an issue occurs because of the hostbridge emulation. Yet, I am still 
> not fully convinced adding an option is worth it.
> Jan and others, any opinions?

Well, if there's a proper fallback, then why not allow using it in
case of problems?




Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.