Re: [PATCH v14 3/9] fw_cfg: fix sparse warnings in fw_cfg_sel_endianness()

[Marc-Andre Lureau]

On Wed, Feb 14, 2018 at 9:46 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> On Wed, Feb 14, 2018 at 03:18:44PM +0100, Marc-Andrà Lureau wrote:
>> The function is used for both LE & BE target type, use __force casting.
>>
>> Fixes:
>> $ make C=1 CF=-D__CHECK_ENDIAN__ drivers/firmware/qemu_fw_cfg.o
>>
>> drivers/firmware/qemu_fw_cfg.c:55:33: warning: restricted __be16 degrades to integer
>> drivers/firmware/qemu_fw_cfg.c:55:52: warning: restricted __le16 degrades to integer
>>
>> Signed-off-by: Marc-Andrà Lureau <marcandre.lureau@xxxxxxxxxx>
>> ---
>>  drivers/firmware/qemu_fw_cfg.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
>> index 90f467232777..85e693287d87 100644
>> --- a/drivers/firmware/qemu_fw_cfg.c
>> +++ b/drivers/firmware/qemu_fw_cfg.c
>> @@ -52,7 +52,9 @@ static DEFINE_MUTEX(fw_cfg_dev_lock);
>>  /* pick appropriate endianness for selector key */
>>  static inline u16 fw_cfg_sel_endianness(u16 key)
>>  {
>> -     return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
>> +     return fw_cfg_is_mmio ?
>> +             (u16 __force)cpu_to_be16(key) :
>> +             (u16 __force)cpu_to_le16(key);
>>  }
>>
>>  /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
>
> Well the caller does cpu_to_le16 on the result ...
> All this makes my head spin.
>
> IMHO what you want is a wrapper that does iowrite and iowritebe
> rather than __force.

iowrite16(key) is the same as iowrite16(cpu_to_le16(key)) ? There is
no iowrite16le()...

Is this equivalent, and not introducing regressions?

static inline u16 fw_cfg_sel_endianness(u16 key)
+static void fw_cfg_sel_endianness(u16 key)
 {
-       return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
+       if (fw_cfg_is_mmio)
+               iowrite16be(key, fw_cfg_reg_ctrl);
+       else
+               iowrite16(key, fw_cfg_reg_ctrl);
 }

 /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
@@ -74,7 +77,7 @@ static inline void fw_cfg_read_blob(u16 key,
        }

        mutex_lock(&fw_cfg_dev_lock);
-       iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
+       fw_cfg_sel_endianness(key);

>
>
>> --
>> 2.16.1.73.g5832b7e9f2