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SubjectRe: [PATCH] staging: pi433: add descriptions for mutex locks
On Fri, Mar 23, 2018 at 04:38:50PM +0100, Marcus Wolf wrote:
> I had no time to work on the code for monthes now and the memorisation
> of my thoughts when I was programming that (approx. one year ago) is
> quite pale.
>
> As far as I remember, I read something, that the fifo has an integrated
> protection, so no external protection is needed. But absolutely unsure.
>
> If I will find some time within the next days, I'll have a look at the
> code and try to recall.
>
> But the most important thing already took place: We started thinking
> about it :-)

You are right, here is what kfifo.h says:

/*
* Note about locking : There is no locking required until only * one reader
* and one writer is using the fifo and no kfifo_reset() will be * called
* kfifo_reset_out() can be safely used, until it will be only called
* in the reader thread.
* For multiple writer and one reader there is only a need to lock the writer.
* And vice versa for only one writer and multiple reader there is only a need
* to lock the reader.
*/

In the case of pi433 there is only one reader (pi433_tx_thread) and
there is no need for a lock there. But the char device (pi433_write)
might have multiple writers so we leave the mutex just in that function?

--
Valentin

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