Re: [PATCH 2/3] hwrng: stm32 - add support for STM32 HW RNG
From: Daniel Thompson <hidden>
Date: 2015-10-11 19:24:12
Also in:
linux-arm-kernel, linux-devicetree, lkml
On 5 October 2015 at 10:22, Daniel Thompson [off-list ref] wrote:
On 4 October 2015 at 11:32, Linus Walleij [off-list ref] wrote:quoted
On Sat, Oct 3, 2015 at 10:35 PM, Daniel Thompson [off-list ref] wrote: Then this construct:quoted
+static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait) +{(...)quoted
+ /* enable random number generation */ + clk_enable(priv->clk); + cr = readl(priv->base + RNG_CR); + writel(cr | RNG_CR_RNGEN, priv->base + RNG_CR);(...)quoted
+ /* disable the generator */ + writel(cr, priv->base + RNG_CR); + clk_disable(priv->clk);This is in the hotpath where megabytes of data may be read out by consecutive reads. I think it's wise to move the clock enable/disable and also the write to cr to enable/disable the block to runtime PM hooks, so that you can e.g. set some hysteresis around the disablement with pm_runtime_set_autosuspend_delay(&dev->dev, 50); pm_runtime_use_autosuspend(&dev->dev);pm_runtime_put_autosuspend(). For a primecell check the usage in drivers/mmc/host/mmci.c for a complex usecase or e.g. drivers/hwtracing/coresight/coresight-tpiu.c for a simpler usecase. For the performance hints I guess you can even test whether what I'm saying makes sense or not by reading some megabytes of random and timing it.I'll have to benchmark this. clk_enable/disable have pretty simple implementations on STM32 so there might not be much in it.
Well... I was extremely wrong about that! Switching the driver over to autosuspend yielded a very significant performance boost: ~1.1MiB/s to ~1.5MiB/s . Very pleased with that! Daniel.