Re: [PATCH] rt2x00: improve calling conventions for register accessors

Arnd Bergmann
2017-05-16T14:19:28Z

On Tue, May 16, 2017 at 3:44 PM, Jes Sorensen <jes.sorensen@gmail.com> wrote:
> On 05/16/2017 07:55 AM, Stanislaw Gruszka wrote:
>>
>> On Mon, May 15, 2017 at 10:39:51AM -0400, David Miller wrote:
>>>
>>> Passing return values by reference is and always has been a really
>>> poor way to achieve what these functions are doing.
>>>
>>> And frankly, whilst the tool could see what's going on here better, we
>>> should be making code easier rather than more difficult to audit.
>>>
>>> I am therefore very much in favor of Arnd's change.
>>>
>>> This isn't even a situation where there are multiple return values,
>>> such as needing to signal an error and return an unsigned value at the
>>> same time.
>>>
>>> These functions return _one_ value, and therefore they should be
>>> returned as a true return value.
>>
>>
>> In rt2x00 driver we use poor convention in other kind of registers
>> accessors like bbp, mac, eeprom. I dislike to changing only rfcsr
>> accessors and leaving others in the old way. And changing all accessors
>> would be massive and error prone change, which I'm not prefer either.
>
>
> That's why you do it in multiple smaller patches rather than one ugly giant
> patch.

I did the first step using a search&replace in vim using

s:\(rt2800_rfcsr_read(.*,.*\), &\(.*\));:\2 = \1);:

but had to introduce a conversion function

static void rt2800_rfcsr_readreg(struct rt2x00_dev *rt2x00dev,
const unsigned int word, u8 *value)
{
*value = rt2800_rfcsr_read(rt2x00dev, word);
}

to keep the correct types in place for struct rt2x00debug. I now
did all the other ones too, and removed that helper again. The
result in much nicer, but I basically ended up having to do
the same regex search for all of these at once:

static void rt2400pci_bbp_read(struct rt2x00_dev *rt2x00dev,
static void rt2500pci_bbp_read(struct rt2x00_dev *rt2x00dev,
static void rt2500usb_register_read(struct rt2x00_dev *rt2x00dev,
static void rt2500usb_register_read_lock(struct rt2x00_dev *rt2x00dev,
static void rt2500usb_bbp_read(struct rt2x00_dev *rt2x00dev,
static void _rt2500usb_register_read(struct rt2x00_dev *rt2x00dev,
static void rt2800_bbp_read(struct rt2x00_dev *rt2x00dev,
static void rt2800_eeprom_read(struct rt2x00_dev *rt2x00dev,
static void rt2800_rfcsr_readreg(struct rt2x00_dev *rt2x00dev,
static void rt2800_bbp_dcoc_read(struct rt2x00_dev *rt2x00dev,
void (*register_read)(struct rt2x00_dev *rt2x00dev,
void (*register_read_lock)(struct rt2x00_dev *rt2x00dev,
static inline void rt2800_register_read(struct rt2x00_dev *rt2x00dev,
static inline void rt2800_register_read_lock(struct rt2x00_dev *rt2x00dev,
static inline void rt2x00_rf_read(struct rt2x00_dev *rt2x00dev,
static inline void rt2x00_eeprom_read(struct rt2x00_dev *rt2x00dev,
void (*read)(struct rt2x00_dev *rt2x00dev, \
static inline void rt2x00mmio_register_read(struct rt2x00_dev *rt2x00dev,
static inline void _rt2x00_desc_read(__le32 *desc, const u8 word, __le32 *value)
static inline void rt2x00_desc_read(__le32 *desc, const u8 word, u32 *value)
static inline void rt2x00usb_register_read(struct rt2x00_dev *rt2x00dev,
static inline void rt2x00usb_register_read_lock(struct rt2x00_dev *rt2x00dev,
static void rt61pci_bbp_read(struct rt2x00_dev *rt2x00dev,
static void rt73usb_bbp_read(struct rt2x00_dev *rt2x00dev,

and that ended up as a 300KB patch [1]. Splitting it up is clearly possibly,
but I fear that would be more error-prone as we then need to add
those helpers for the other debug stuff as well, and remove it again
afterwards.

Arnd

[1] https://pastebin.com/raw/Qis257mG