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Tsirkin" References: <20190606161943.GA9657@paraplu> <20190606141904-mutt-send-email-mst@kernel.org> <20190611072100.GM2725@paraplu> From: Marcel Apfelbaum Message-ID: <199bd9e0-86c6-4ee3-7f00-1a2fe3ff7501@gmail.com> Date: Tue, 11 Jun 2019 13:19:23 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190611072100.GM2725@paraplu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2a00:1450:4864:20::441 Subject: Re: [Qemu-devel] PCI(e): Documentation "io-reserve" and related properties? X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/11/19 10:21 AM, Kashyap Chamarthy wrote: > On Thu, Jun 06, 2019 at 02:20:18PM -0400, Michael S. Tsirkin wrote: >> On Thu, Jun 06, 2019 at 06:19:43PM +0200, Kashyap Chamarthy wrote: >>> Hi folks, >>> >>> Today I learnt about some obscure PCIe-related properties, in context of >>> the adding PCIe root ports to a guest, namely: >>> >>> io-reserve >>> mem-reserve >>> bus-reserve >>> pref32-reserve >>> pref64-reserve >>> >>> Unfortunately, the commit[*] that added them provided no documentation >>> whatsover. >>> >>> In my scenario, I was specifically wondering about what does >>> "io-reserve" mean, in what context to use it, etc. (But documentation >>> about other properties is also welcome.) >>> >>> Anyone more well-versed in this area care to shed some light? >>> >>> >>> [*] 6755e618d0 (hw/pci: add PCI resource reserve capability to legacy >>> PCI bridge, 2018-08-21) >> So normally bios would reserve just enough io space to satisfy all >> devices behind a bridge. What if you intend to hotplug more devices? >> These properties allow you to ask bios to reserve extra space. > Thanks. Would be useful to have them documented in the official QEMU > command-line documentation. Otherwise, they will remain as arcane > properties that barely anyone knows about. > There is some documentation under qemu/docs/pcie_pci_bridge.txt. I agree there is always room for QEMU cmd-line improvement. Thanks, Marcel