linux-kernel - Re: [PATCH v11 01/17] Xen: ACPI: Hide UART used by Xen

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Date:	Fri, 15 Apr 2016 14:43:37 +0800
From:	Shannon Zhao <zhaoshenglong@...wei.com>
To:	<linux-arm-kernel@...ts.infradead.org>, <sstabellini@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	<catalin.marinas@....com>, <will.deacon@....com>,
	<julien.grall@....com>, <david.vrabel@...rix.com>,
	<xen-devel@...ts.xen.org>, <devicetree@...r.kernel.org>,
	<linux-efi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<shannon.zhao@...aro.org>, <peter.huangpeng@...wei.com>,
	Len Brown <lenb@...nel.org>, open list:
	ACPI <linux-acpi@...r.kernel.org>, ;
Subject: Re: [PATCH v11 01/17] Xen: ACPI: Hide UART used by Xen

Hi Rafael，

Could you please give your comments on this patch? Thanks in advanced!

On 2016/4/7 20:03, Shannon Zhao wrote:
> From: Shannon Zhao <shannon.zhao@...aro.org>
> 
> 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" <rjw@...ysocki.net> (supporter:ACPI)
> CC: Len Brown <lenb@...nel.org> (supporter:ACPI)
> CC: linux-acpi@...r.kernel.org (open list:ACPI)
> Signed-off-by: Shannon Zhao <shannon.zhao@...aro.org>
> ---
>  drivers/acpi/scan.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 74 insertions(+)
> 
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 5f28cf7..cfc73fe 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -46,6 +46,13 @@ DEFINE_MUTEX(acpi_device_lock);
>  LIST_HEAD(acpi_wakeup_device_list);
>  static DEFINE_MUTEX(acpi_hp_context_lock);
>  
> +/*
> + * The UART device described by the SPCR table is the only object which needs
> + * special-casing. Everything else is covered by ACPI namespace paths in STAO
> + * table.
> + */
> +static u64 spcr_uart_addr;
> +
>  struct acpi_dep_data {
>  	struct list_head node;
>  	acpi_handle master;
> @@ -1453,6 +1460,41 @@ 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;
> +
> +	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 && acpi_has_method(handle, METHOD_NAME__CRS)))
> +		return false;
> +
> +	/*
> +	 * The UART device described in SPCR table is assumed to have only one
> +	 * memory resource present. So we only look for the first one here.
> +	 */
> +	status = acpi_walk_resources(handle, METHOD_NAME__CRS,
> +				     acpi_get_resource_memory, &res);
> +	if (ACPI_FAILURE(status) || res.start != spcr_uart_addr)
> +		return false;
> +
> +	acpi_handle_info(handle, "The UART device @%pa in SPCR table will be hidden\n",
> +			 &res.start);
> +
> +	return true;
> +}
> +
>  static int acpi_bus_type_and_status(acpi_handle handle, int *type,
>  				    unsigned long long *sta)
>  {
> @@ -1466,6 +1508,9 @@ 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 +1961,24 @@ 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 +1994,20 @@ 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.
> 

-- 
Shannon