From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.126.131]:59256 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752260AbcGLI23 (ORCPT ); Tue, 12 Jul 2016 04:28:29 -0400 From: Arnd Bergmann To: Bharat Kumar Gogada Cc: "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Bjorn Helgaas , "Liviu.Dudau@arm.com" , nofooter , "thomas.petazzoni@free-electrons.com" Subject: Re: Purpose of pci_remap_iospace Date: Tue, 12 Jul 2016 10:31:59 +0200 Message-ID: <3927657.6zNCtCntSU@wuerfel> In-Reply-To: <8520D5D51A55D047800579B094147198258B85DC@XAP-PVEXMBX01.xlnx.xilinx.com> References: <8520D5D51A55D047800579B094147198258B85DC@XAP-PVEXMBX01.xlnx.xilinx.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: linux-pci-owner@vger.kernel.org List-ID: On Tuesday, July 12, 2016 6:57:10 AM CEST Bharat Kumar Gogada wrote: > Hi, > > I have a query. > > Can any once explain the purpose of pci_remap_iospace function in root port driver. > > What is its dependency with architecture ? > > Here is my understanding, the above API takes PCIe IO resource and its to be mapped CPU address from > ranges property and remaps into virtual address space. > > So my question is who uses this virtual addresses ? The inb()/outb() functions declared in asm/io.h > When End Point requests for IO BARs doesn't it get > from the above resource range (first parameter of API) and > do ioremap to access this region ? Device drivers generally do not ioremap() the I/O BARs but they use inb()/outb() directly. They can also call pci_iomap() and do ioread8()/iowrite8() on the pointer returned from that function, but generally the call to pci_iomap() then returns a pointer into the virtual address that is already mapped. > But why root complex driver is mapping this address region ? The PCI core does not know that the I/O space is memory mapped. On x86 and a few others, I/O space is not memory mapped but requires the use of special CPU instructions. Arnd