On Tue, Sep 01, 2015 at 11:46:19AM +0100, Qais Yousef wrote: > On 08/29/2015 11:18 AM, Mark Brown wrote: > >On Thu, Aug 27, 2015 at 04:40:09PM +0100, Qais Yousef wrote:
Again, please delete unneeded contexts and leave blanks between paragraphs (I notice you've even been removing the blank lines from quoted material). > >>>>+#define PIPE_STARTED 1 > >>>>+#define PIPE_RUNNING 2 > >>>Why is the case with in place buffers not a simple zero iteration loop? > >>This is important when AXD is not consuming the data through I2S and > >>returning them to Linux. What we're trying to deal with here is the firmware > >>processed some data and expects Linux to consume whatever it has sent back > >>to it. We want to ensure that if the user suddenly stopped consuming this > >>data by closing the pipe to drop anything we receive back from AXD otherwise > >>the workqueue would block indefinitely waiting for the user that disappeared > >>to consume it causing a deadlock. > >That doesn't seem to address the question... > I'm sorry I don't understand your question then. Can you rephrase it please? Why don't we just always try to consume any buffers that are in flight? > >Why not just reuse the bufferq implementation if that's what you want to > >use? More generally most audio ring buffers just keep track of the last > >place read or written and don't bother with semaphores (why do we even > >need to block?). It's not just the semaphore you're using here but also > >some non-atomic variables accessed with memory barriers and mutexes all > >scattered over a very large block of code. It is far too much effort to > >reason about what the locking scheme is supposed to be here to determine > >if it is safe, and that's not going to get any easier when reviewing > >future changes. > We need to block because in the past at least the driver could work on > blocking mode and it would return the buffers back to Linux and there was no > guarantee that the reader and writer would be on the same rate. The worst > case assumption was that the writer and the reader could be 2 different > apps. For example an app getting data from network to AXD to be encoded and > another app reading the encoded data to store it on disk. And AXD supports > multi-pipeline, so more one of these operations could be happening at the > same time. I can't really connect the above with a need to block, sorry... I'm going to assume this was something to do with old non-standard external interfaces.
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