Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753020AbcCZNPh (ORCPT ); Sat, 26 Mar 2016 09:15:37 -0400 Received: from smtp.citrix.com ([66.165.176.89]:39491 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751846AbcCZNPf (ORCPT ); Sat, 26 Mar 2016 09:15:35 -0400 X-IronPort-AV: E=Sophos;i="5.24,396,1454976000"; d="scan'208";a="342321527" Date: Sat, 26 Mar 2016 13:14:20 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: "Rafael J. Wysocki" CC: Shannon Zhao , , , , , , , , , , , , Len Brown , "open list:ACPI" Subject: Re: [PATCH v8 01/17] Xen: ACPI: Hide UART used by Xen In-Reply-To: <7418231.W9aSFKr1zs@vostro.rjw.lan> Message-ID: References: <1458830676-27075-2-git-send-email-shannon.zhao@linaro.org> <1458893149-17388-1-git-send-email-zhaoshenglong@huawei.com> <7418231.W9aSFKr1zs@vostro.rjw.lan> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4795 Lines: 146 On Fri, 25 Mar 2016, Rafael J. Wysocki wrote: > On Friday, March 25, 2016 04:05:49 PM Shannon Zhao wrote: > > From: Shannon Zhao > > > > ACPI 6.0 introduces a new table STAO to list the devices which are used > > by Xen and can't be used by Dom0. On Xen virtual platforms, the physical > > UART is used by Xen. So here it hides UART from Dom0. > > > > CC: "Rafael J. Wysocki" (supporter:ACPI) > > CC: Len Brown (supporter:ACPI) > > CC: linux-acpi@vger.kernel.org (open list:ACPI) > > Signed-off-by: Shannon Zhao > > So I said it looked good, but now that I think about it, I have a question. -> > > > --- > > drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 68 insertions(+) > > > > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c > > index 5f28cf7..5420cc5 100644 > > --- a/drivers/acpi/scan.c > > +++ b/drivers/acpi/scan.c > > @@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list); > > DEFINE_MUTEX(acpi_device_lock); > > LIST_HEAD(acpi_wakeup_device_list); > > static DEFINE_MUTEX(acpi_hp_context_lock); > > +static u64 spcr_uart_addr; > > > > struct acpi_dep_data { > > struct list_head node; > > @@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child, > > return 0; > > } > > > > +static acpi_status acpi_get_resource_memory(struct acpi_resource *ares, > > + void *context) > > +{ > > + struct resource *res = context; > > + > > + if (acpi_dev_resource_memory(ares, res)) > > + return AE_CTRL_TERMINATE; > > -> It looks like this will terminate on the first memory resource found, > but what if there are more of them? > > Or is it guaranteed that there will be only one for the device objects in > question? Given that spcr_uart_addr is actually the only Base Address specified by the SPCR table, I think it is assumed that this kind of devices only have one memory region. > If not, then it would better to check res.start == spcr_uart_addr here too > and only terminate if there's a match. > > > + > > + return AE_OK; > > +} > > + > > +static bool acpi_device_should_be_hidden(acpi_handle handle) > > +{ > > + acpi_status status; > > + struct resource res; > > + > > + /* Check if it should ignore the UART device */ > > + if (spcr_uart_addr != 0) { > > + if (!acpi_has_method(handle, METHOD_NAME__CRS)) > > + return false; > > + > > + status = acpi_walk_resources(handle, METHOD_NAME__CRS, > > + acpi_get_resource_memory, &res); > > + if (ACPI_FAILURE(status)) > > + return false; > > + > > + if (res.start == spcr_uart_addr) { > > + printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n"); > > + return true; > > + } > > + } > > + > > + return false; > > +} > > + > > static int acpi_bus_type_and_status(acpi_handle handle, int *type, > > unsigned long long *sta) > > { > > @@ -1466,6 +1502,9 @@ static int acpi_bus_type_and_status(acpi_handle handle, int *type, > > switch (acpi_type) { > > case ACPI_TYPE_ANY: /* for ACPI_ROOT_OBJECT */ > > case ACPI_TYPE_DEVICE: > > + if (acpi_device_should_be_hidden(handle)) > > + return -ENODEV; > > + > > *type = ACPI_BUS_TYPE_DEVICE; > > status = acpi_bus_get_status_handle(handle, sta); > > if (ACPI_FAILURE(status)) > > @@ -1916,9 +1955,24 @@ static int acpi_bus_scan_fixed(void) > > return result < 0 ? result : 0; > > } > > > > +static void __init acpi_get_spcr_uart_addr(void) > > +{ > > + acpi_status status; > > + struct acpi_table_spcr *spcr_ptr; > > + > > + status = acpi_get_table(ACPI_SIG_SPCR, 0, > > + (struct acpi_table_header **)&spcr_ptr); > > + if (ACPI_SUCCESS(status)) > > + spcr_uart_addr = spcr_ptr->serial_port.address; > > + else > > + printk(KERN_WARNING PREFIX "STAO table present, but SPCR is missing\n"); > > +} > > + > > int __init acpi_scan_init(void) > > { > > int result; > > + acpi_status status; > > + struct acpi_table_stao *stao_ptr; > > > > acpi_pci_root_init(); > > acpi_pci_link_init(); > > @@ -1934,6 +1988,20 @@ int __init acpi_scan_init(void) > > > > acpi_scan_add_handler(&generic_device_handler); > > > > + /* > > + * If there is STAO table, check whether it needs to ignore the UART > > + * device in SPCR table. > > + */ > > + status = acpi_get_table(ACPI_SIG_STAO, 0, > > + (struct acpi_table_header **)&stao_ptr); > > + if (ACPI_SUCCESS(status)) { > > + if (stao_ptr->header.length > sizeof(struct acpi_table_stao)) > > + printk(KERN_INFO PREFIX "STAO Name List not yet supported."); > > + > > + if (stao_ptr->ignore_uart) > > + acpi_get_spcr_uart_addr(); > > + } > > + > > mutex_lock(&acpi_scan_lock); > > /* > > * Enumerate devices in the ACPI namespace. > > >