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. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html