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Re: [PATCH 5/6] acpi: serial: don't use _STA method


From: Igor Mammedov
Subject: Re: [PATCH 5/6] acpi: serial: don't use _STA method
Date: Fri, 27 Mar 2020 15:33:40 +0100

On Fri, 27 Mar 2020 13:11:10 +0100
Gerd Hoffmann <address@hidden> wrote:

> The _STA method dates back to the days where we had a static DSDT.  The
> device is listed in the DSDT table unconditionally and the _STA method
> checks a bit in the isa bridge pci config space to figure whenever a
> given is isa device is present or not, then evaluates to 0x0f (present)
> or 0x00 (absent).
> 
> These days the DSDT is generated by qemu anyway, so if a device is not
> present we can simply drop it from the DSDT instead.
> 
> Signed-off-by: Gerd Hoffmann <address@hidden>
> ---
>  hw/i386/acpi-build-pc.c | 32 ++++++++------------------------
>  1 file changed, 8 insertions(+), 24 deletions(-)
> 
> diff --git a/hw/i386/acpi-build-pc.c b/hw/i386/acpi-build-pc.c
> index 18ca2fd46961..97af5eac3d79 100644
> --- a/hw/i386/acpi-build-pc.c
> +++ b/hw/i386/acpi-build-pc.c
> @@ -1204,50 +1204,34 @@ static Aml *build_lpt_device_aml(void)
>      return dev;
>  }
>  
> -static Aml *build_com_device_aml(uint8_t uid)
> +static void build_com_device_aml(Aml *scope, uint8_t uid)
>  {
>      Aml *dev;
>      Aml *crs;
> -    Aml *method;
> -    Aml *if_ctx;
> -    Aml *else_ctx;
> -    Aml *zero = aml_int(0);
> -    Aml *is_present = aml_local(0);
> -    const char *enabled_field = "CAEN";
>      uint8_t irq = 4;
>      uint16_t io_port = 0x03F8;
>  
>      assert(uid == 1 || uid == 2);
>      if (uid == 2) {
> -        enabled_field = "CBEN";
>          irq = 3;
>          io_port = 0x02F8;
>      }
> +    if (!memory_region_present(get_system_io(), io_port)) {
                                  ^^^^^^
even though acpi_setup() is a part of board code, usually it's not recommended 
to 
use get_system_foo() outside of machine_init()

how about fishing out present serial ports from isa device in a helper
like acpi_get_misc_info(), and then generalize AML like
   build_com_device_aml(Aml *scope, uint8_t uid, io_port, irq)
   

> +        return;
> +    }
>  
>      dev = aml_device("COM%d", uid);
>      aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0501")));
>      aml_append(dev, aml_name_decl("_UID", aml_int(uid)));
>  
> -    method = aml_method("_STA", 0, AML_NOTSERIALIZED);
> -    aml_append(method, aml_store(aml_name("%s", enabled_field), is_present));
> -    if_ctx = aml_if(aml_equal(is_present, zero));
> -    {
> -        aml_append(if_ctx, aml_return(aml_int(0x00)));
> -    }
> -    aml_append(method, if_ctx);
> -    else_ctx = aml_else();
> -    {
> -        aml_append(else_ctx, aml_return(aml_int(0x0f)));
> -    }
> -    aml_append(method, else_ctx);
> -    aml_append(dev, method);
> +    aml_append(dev, aml_name_decl("_STA", aml_int(0xf)));
>  
>      crs = aml_resource_template();
>      aml_append(crs, aml_io(AML_DECODE16, io_port, io_port, 0x00, 0x08));
>      aml_append(crs, aml_irq_no_flags(irq));
>      aml_append(dev, aml_name_decl("_CRS", crs));
>  
> -    return dev;
> +    aml_append(scope, dev);
>  }
>  
>  static void build_isa_devices_aml(Aml *table)
> @@ -1265,8 +1249,8 @@ static void build_isa_devices_aml(Aml *table)
>          aml_append(scope, build_fdc_device_aml(fdc));
>      }
>      aml_append(scope, build_lpt_device_aml());
> -    aml_append(scope, build_com_device_aml(1));
> -    aml_append(scope, build_com_device_aml(2));
> +    build_com_device_aml(scope, 1);
> +    build_com_device_aml(scope, 2);
>  
>      if (ambiguous) {
>          error_report("Multiple ISA busses, unable to define IPMI ACPI data");




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