From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Date: Wed, 03 Aug 2016 05:12:16 +0000 Subject: Re: Assign BAR address for pci device after hotplug Message-Id: <20160803051216.GA4515@kroah.com> List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-hotplug@vger.kernel.org On Tue, Aug 02, 2016 at 09:11:09PM +0000, Chitturi, Divakar wrote: > Hi > > Below are two scenarios for which i would like to understand the right > way to assign the BAR address for my PCI device > > Device details: > pci switch upstrem port connected to root complex > pci switch downstream port 1 connected to my_pci_device > my_pci_device is FPGA > FPGA has bunch of controllers and other logic > > Driver details: > Have a dedicated pci kernel driver for my_device > Enabled pcihp kernel driver Which pci hotplug driver? Just the PCI Hotplug core isn't going to do anything, you need a controller driver for your specific PCI hotplug hardware. > At power on, BIOS assigns/reserves specific region of memory for my pci device. > during the linux boot process, pci core will assign the bar and other initialization and call my > probe function in the driver. probe function will perform some initialization which includes reading > the BAR and setting some registers in IO space of the device. > > Scn1: > At some point the device is removed and reinserted > > Scn2: > At some point similar device is inserted in a new pci slot How are they added/removed without a hotplug controller? > In both the scenarios explained about, BIOS is not involved as system was never turned off completely. So > 1. how do we obtain the BAR address for the device. What architecture is this? x86? If so, it just uses whatever the BIOS said was there for the last time. > 2. Should i assign it explicitly? Yes. > 3. if yes, should it be done in my driver ( in both the case i am assuming driver's probe function will be called ) No, in your pci hotplug driver, you need to handle it there. > 4. can i use pci_assign_resource() in drivers probe function Nope. > 5. is something like below the right way to do it ? > > static int my_probe(struct pci_dev *pdev, const struct pci_device_id *id) > { > if( pci_resource_start (pdev,BAR0) <= 0) { > pr_debug(" Assign BAR0 \n"); > ret = pci_assign_resource(pdev,BAR0); > if( 0 > ret) { > dev_err(&pdev->dev, " Failed to assign resource \n"); > return ret; > } > } > > ret = pci_enable_device(pdev); > ret = pci_request_regions(pdev, dev_driver_string(&pdev->dev)); > base_addr = pci_iomap(pdev, BAR0, 0); > } You need to write a pci hotplug controller driver to manage the resources and assign them properly. That's its responsibility, see the PCI hotplug specification for all of the details... good luck! greg k-h