dmatest: replace stored results mechanism, with uniform messages

For long running tests the tracking results in a memory leak for the "ok"
results, and for the failures the kernel log should be sufficient.  Provide a
uniform format for error messages so they can be easily parsed and remove the
debugfs file.

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/dmatest.txt

@@ -16,9 +16,8 @@ be built as module or inside kernel. Let's consider those cases.
 	Part 2 - When dmatest is built as a module...
 
 After mounting debugfs and loading the module, the /sys/kernel/debug/dmatest
-folder with nodes will be created. There are two important files located. First
-is the 'run' node that controls run and stop phases of the test, and the second
-one, 'results', is used to get the test case results.
+folder with a file named 'run' nodes will be created.  'run' controls run and
+stop phases of the test.
 
 Note that in this case test will not run on load automatically.
 
@@ -32,8 +31,9 @@ Hint: available channel list could be extracted by running the following
 command:
 	% ls -1 /sys/class/dma/
 
-After a while you will start to get messages about current status or error like
-in the original code.
+Once started a message like "dmatest: Started 1 threads using dma0chan0" is
+emitted.  After that only test failure messages are reported until the test
+stops.
 
 Note that running a new test will not stop any in progress test.
 
@@ -62,19 +62,18 @@ case. You always could check them at run-time by running
 
 	Part 4 - Gathering the test results
 
-The module provides a storage for the test results in the memory. The gathered
-data could be used after test is done.
+Test results are printed to the kernel log buffer with the format:
 
-The special file 'results' in the debugfs represents gathered data of the in
-progress test. The messages collected are printed to the kernel log as well.
+"dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
 
 Example of output:
-	% cat /sys/kernel/debug/dmatest/results
-	dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
+	% dmesg | tail -n 1
+	dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
 
 The message format is unified across the different types of errors. A number in
 the parens represents additional information, e.g. error code, error counter,
-or status.
+or status.  A test thread also emits a summary line at completion listing the
+number of tests executed, number that failed, and a result code.
 
-Note that the buffer comparison is done in the old way, i.e. data is not
-collected and just printed out.
+The details of a data miscompare error are also emitted, but do not follow the
+above format.