msm: bam_dmux: tune downlink polling parameters

This change disables the BAM DMUX adaptive timer - this is to address
concerns about drops in TCP throughput for some use cases with the timer
enabled.  It also sets the aggregation to 3ms to save power while not
compromising performance. Power tests show a savings of 3-4% (compared to
having the timer poll the BAM pipe every 1 ms) for LTE (40Mbps downlink and
25Mbps uplink) and HSPA (7Mbps downlink and 384Kbps uplink) with no
degradation in performance.

Change-Id: Ia51eae773723e60d8b051766ad80bfb0a16f5f6d
Signed-off-by: Anurag Singh <anursing@codeaurora.org>
msm: bam_dmux: add loopback support

Bam dmux is currently very difficult to isolate and provide measurements
for common metrics, such as throughput and latency.

Add hooks into bam_dmux to allow for a seperate dynamically
loadable loopback module. This allows bam dmux to be isolated, and to
provide more accurate measurements of the above metrics.

Change-Id: I174d900dea73cca27d32a54a908f43728059be30
Signed-off-by: Brent Hronik <bhronik@codeaurora.org>
msm: bam_dmux: Fix race condition during SSR

BAM DMUX drivers set the global flags to identify the SSR during
SUBSYS_BEFORE_SHUTDOWN notification, but the flags change is not reflected
in some code paths like msm_bam_dmux_write().

Add the SSR flag check and SRCU locking to complete all pending bam dmux
writes before returning the control in SSR call back function for
SUBSYS_BEFORE_SHUTDOWN notification.

CRs-Fixed: 584805
Change-Id: I26647b485977943f272c44f7450ed6c4a4aa62f3
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
msm: bam_dmux: modify DL low memory algorithm

Bam_dmux maintains a pool of dynamically allocated buffers for the BAM DMA
engine to use as destination memory for Downlink (DL) data.  The allocation
requests for the buffers are done using flags to indicate delays are
tolerable and either the memory or an error should be returned immediately
to bam_dmux as the buffers are normally allocated within various hot paths
inside of the driver.  If a low memory allocation failure is encountered
when attempting to replenish the pool of buffers, bam_dmux will either
attempt the memory allocations later when the next scheduled pool refilling
occurs if there is at least one buffer remaining in the pool, or will
schedule a delayed task to retry the buffer allocation until atleast one
buffer can be put into the pool.

This mechanism of handling low memory situations has two flaws.  First, the
allocation type used by bam_dmux does not trigger the standard low memory
recovery mechanism within the memory management subsystem.  Second, the
peripeheral on the otherside do the DMA engine has a limited hardware based
flow control mechanism that will not release flow control with only one
buffer queued to the DMA engine.

To assist in system recovery, and avoid a data stall, create a cold path
that is tolerant of memory allocation delays and is triggered when the hot
path encounters an allocation failure.

CRs-Fixed: 589665
Change-Id: If72b0eaef285ac6dfd99e97bef1cd7df154e3a48
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>