On 2016-04-27 04:47, Marc Zyngier wrote:
On 27/04/16 09:15, Vinod Koul wrote:
On Tue, Apr 26, 2016 at 12:55:18PM -0400, Sinan Kaya wrote:
On 4/26/2016 12:25 PM, Vinod Koul wrote:
On Tue, Apr 26, 2016 at 08:08:16AM -0400, okaya@xxxxxxxxxxxxxx
wrote:
On 2016-04-25 23:30, Vinod Koul wrote:
On Mon, Apr 11, 2016 at 10:21:12AM -0400, Sinan Kaya wrote:
+static int hidma_chan_stats(struct seq_file *s, void *unused)
+{
+ struct hidma_chan *mchan = s->private;
+ struct hidma_desc *mdesc;
+ struct hidma_dev *dmadev = mchan->dmadev;
+
+ pm_runtime_get_sync(dmadev->ddev.dev);
debug shouldn't power up device, why do you want to do that
Clocks are turned off while the hw is idle. I can’t reach hw
registers without restoring power.
Hmm, have you thought about using regmap?
To be honest, I didn't know what regmap is but I just read some code
and looked at how it is used. Feel free to correct me if I got it
wrong.
Regmap seems to be designed for *slow* speed peripherals to improve
frequent
accesses by the SW. It looks like it is used by MFD, SPI and I2C
drivers.
It seems to cache the register contents and flush/invalidate them
only when
needed.
The MMIO version seems to be assuming the presence of device-tree
like CLK
API which doesn't exist on ACPI systems and is not portable.
My reaction is that it is a lot of code with no added functionality
to what
HIDMA driver is trying to achieve.
Given that the use case here is only for debug purposes; I think it
is OK
to keep this runtime call here. I don't want to add any overhead into
the
existing code just to support the debug use case.
None of my register read/writes are slow. This file will only be used
to
troubleshoot customer issues.
I'd recommend you actually run perf on a a few of your MMIO accesses. I
believe the result will be eye opening. On the KVM side, we've trimmed
our MMIO access as much as possible, using a memory-based cache
(similar
to regmap in concept). This has made some code paths about 40% faster.
$ is always faster than MMIO. This way you can give reg contents to
users
without waking up hw.
Indeed. MMIO access sucks rocks, even on a very fast box. Actually, the
faster the box is, the slower MMIO feels (compared to memory).
Thanks,
M.
Agreed. However, I need to understand how regmap really works under the
covers and whether it is compatible with the hardware.
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