On Thursday 10 March 2011, Waldemar.Rymarkiewicz@xxxxxxxxx wrote:
> >What I suggest you do is to work with the maintainers of the existing
> >pn544 driver (Matti and Jari) to create an NFC core library
> >that takes care of the character device interface and that can
> >be shared between the two drivers. Instead of each driver
> >registering a misc device, make it call a
> >nfc_device_register() function that is implemented in a common module.
>
> I've been already thinking about that and it's seems like next obvious step.
Ok, cool.
> >mdev, rx_waitq and mutex would go into the common module.
> >I would expect that you also need a tx_waitq. What happens
> >when the buffer is full?
>
> Do you mean info->buff ?
Oh, I see you simply do
ret = i2c_master_send(client, info->buf, len);
usleep_range(1000, 10000);
and assume that the buffer can always be written within a milisecond,
so you just slow down output enough to never have to worry about it,
right?
A nicer solution would be to have an interrupt driven output
so you know when the i2c buffers have been flushed.
> >Note that the microread_is_busy() logic does not protect you
> >from having multiple concurrent readers, because multiple
> >threads may share a single file descriptor.
>
> It's just used to ensure that only one reader can open the device.
> It's called only in open callback.
> The mutex actually secures concurrent read operations.
So if having multiple readers is safe (though possibly not
meaningful), I guess you don't really need the microread_is_busy()
logic.
I suppose it doesn't hurt either, it just seems a bit pointless
when it does the right thing most of the time, but not always.
Arnd
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