linux-kernel - Re: [PATCH] ACPI: SPCR: Use access width to determine mmio usage

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Date:   Fri, 5 May 2017 17:54:24 -0400
From:   Jon Mason <jon.mason@...adcom.com>
To:     "Zheng, Lv" <lv.zheng@...el.com>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, Len Brown <lenb@...nel.org>,
        "Moore, Robert" <robert.moore@...el.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH] ACPI: SPCR: Use access width to determine mmio usage

On Thu, May 4, 2017 at 11:09 PM, Zheng, Lv <lv.zheng@...el.com> wrote:
> Hi,
>
>> From: Jon Mason [mailto:jon.mason@...adcom.com]
>> Sent: Thursday, May 4, 2017 11:06 PM
>> Subject: [PATCH] ACPI: SPCR: Use access width to determine mmio usage
>>
>> The current SPCR code does not check the access width of the mmio, and
>> uses a default of 8bit register accesses.  This prevents devices that
>> only do 16 or 32bit register accesses from working.  By simply checking
>> this field and setting the mmio string appropriately, this issue can be
>> corrected.  To prevent any legacy issues, the code will default to 8bit
>> accesses if the value is anything but 16 or 32.
>>
>> Signed-off-by: Jon Mason <jon.mason@...adcom.com>
>> ---
>>  drivers/acpi/spcr.c     | 18 ++++++++++++++++--
>>  include/acpi/acrestyp.h |  7 +++++++
>>  2 files changed, 23 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
>> index 01c9466..11233f6 100644
>> --- a/drivers/acpi/spcr.c
>> +++ b/drivers/acpi/spcr.c
>> @@ -74,8 +74,22 @@ int __init parse_spcr(bool earlycon)
>>               goto done;
>>       }
>>
>> -     iotype = table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY ?
>> -                     "mmio" : "io";
>> +     if (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
>> +             switch (table->serial_port.access_width) {
>> +             default:
>> +                     pr_err("Unexpected SPCR Access Width.  Defaulting to byte size\n");
>> +             case ACPI_ACCESS_SIZE_BYTE:
>> +                     iotype = "mmio";
>> +                     break;
>> +             case ACPI_ACCESS_SIZE_WORD:
>> +                     iotype = "mmio16";
>> +                     break;
>> +             case ACPI_ACCESS_SIZE_DWORD:
>> +                     iotype = "mmio32";
>> +                     break;
>> +             }
>> +     } else
>> +             iotype = "io";
>>
>>       switch (table->interface_type) {
>>       case ACPI_DBG2_ARM_SBSA_32BIT:
>> diff --git a/include/acpi/acrestyp.h b/include/acpi/acrestyp.h
>> index f0f7403..781cb55 100644
>> --- a/include/acpi/acrestyp.h
>> +++ b/include/acpi/acrestyp.h
>> @@ -372,6 +372,13 @@ struct acpi_resource_generic_register {
>>       u64 address;
>>  };
>>
>> +/* Generic Address Space Access Sizes */
>> +#define ACPI_ACCESS_SIZE_UNDEFINED           0
>> +#define ACPI_ACCESS_SIZE_BYTE                        1
>> +#define ACPI_ACCESS_SIZE_WORD                        2
>> +#define ACPI_ACCESS_SIZE_DWORD                       3
>> +#define ACPI_ACCESS_SIZE_QWORD                       4
>> +
>>  struct acpi_resource_gpio {
>>       u8 revision_id;
>>       u8 connection_type;
>
> Please don't define this.
> It's possible to calculate 8/16/32/64 from the access width value.
> Try:
> 1 << (access_width + 2）

Thanks, I'll send out v2 of the patch with this change.

> Thanks
> Lv
>