From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Message-ID: <1503256100.12059.13.camel@kernel.crashing.org> Subject: Re: [PATCH v2 1/1] Split VGA default device handler out of VGA arbiter From: Benjamin Herrenschmidt To: Bjorn Helgaas , Daniel Axtens Cc: linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, gabriele.paoloni@huawei.com, airlied@linux.ie, will.deacon@arm.com, dri-devel@lists.freedesktop.org, z.liuxinliang@hisilicon.com, bhelgaas@google.com, alex.williamson@redhat.com, lukas@wunner.de, catalin.marinas@arm.com, zourongrong@gmail.com, daniel.vetter@intel.com Date: Sun, 20 Aug 2017 12:08:20 -0700 In-Reply-To: <20170819154753.GQ28977@bhelgaas-glaptop.roam.corp.google.com> References: <20170817113028.16853-1-dja@axtens.net> <20170817113028.16853-2-dja@axtens.net> <20170819154753.GQ28977@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-ID: On Sat, 2017-08-19 at 10:47 -0500, Bjorn Helgaas wrote: > So if ARM64 doesn't have these PCI legacy resources, does that mean an > ARM64 host bridge cannot generate these legacy addresses on PCI? That > is, there's no host bridge window that maps to those PCI addresses? > That seems like a curious restriction on host bridges, but I guess it > would be possible. It's rather common. For example on POWER8: - There is no IO space at all - We configure the 32-bit MMIO window to be around 3..4G (to avoid overlapping with DMA space below it). So we effectively have no path to the legacy areas, and that hasn't been a problem so far. Cheers, Ben. From mboxrd@z Thu Jan 1 00:00:00 1970 From: benh@kernel.crashing.org (Benjamin Herrenschmidt) Date: Sun, 20 Aug 2017 12:08:20 -0700 Subject: [PATCH v2 1/1] Split VGA default device handler out of VGA arbiter In-Reply-To: <20170819154753.GQ28977@bhelgaas-glaptop.roam.corp.google.com> References: <20170817113028.16853-1-dja@axtens.net> <20170817113028.16853-2-dja@axtens.net> <20170819154753.GQ28977@bhelgaas-glaptop.roam.corp.google.com> Message-ID: <1503256100.12059.13.camel@kernel.crashing.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sat, 2017-08-19 at 10:47 -0500, Bjorn Helgaas wrote: > So if ARM64 doesn't have these PCI legacy resources, does that mean an > ARM64 host bridge cannot generate these legacy addresses on PCI? That > is, there's no host bridge window that maps to those PCI addresses? > That seems like a curious restriction on host bridges, but I guess it > would be possible. It's rather common. For example on POWER8: - There is no IO space at all - We configure the 32-bit MMIO window to be around 3..4G (to avoid overlapping with DMA space below it). So we effectively have no path to the legacy areas, and that hasn't been a problem so far. Cheers, Ben. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [PATCH v2 1/1] Split VGA default device handler out of VGA arbiter Date: Sun, 20 Aug 2017 12:08:20 -0700 Message-ID: <1503256100.12059.13.camel@kernel.crashing.org> References: <20170817113028.16853-1-dja@axtens.net> <20170817113028.16853-2-dja@axtens.net> <20170819154753.GQ28977@bhelgaas-glaptop.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170819154753.GQ28977@bhelgaas-glaptop.roam.corp.google.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Bjorn Helgaas , Daniel Axtens Cc: gabriele.paoloni@huawei.com, airlied@linux.ie, linux-pci@vger.kernel.org, will.deacon@arm.com, dri-devel@lists.freedesktop.org, z.liuxinliang@hisilicon.com, zourongrong@gmail.com, alex.williamson@redhat.com, lukas@wunner.de, catalin.marinas@arm.com, bhelgaas@google.com, daniel.vetter@intel.com, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org List-Id: dri-devel@lists.freedesktop.org On Sat, 2017-08-19 at 10:47 -0500, Bjorn Helgaas wrote: > So if ARM64 doesn't have these PCI legacy resources, does that mean an > ARM64 host bridge cannot generate these legacy addresses on PCI? That > is, there's no host bridge window that maps to those PCI addresses? > That seems like a curious restriction on host bridges, but I guess it > would be possible. It's rather common. For example on POWER8: - There is no IO space at all - We configure the 32-bit MMIO window to be around 3..4G (to avoid overlapping with DMA space below it). So we effectively have no path to the legacy areas, and that hasn't been a problem so far. Cheers, Ben.