On Fri, Aug 31, 2018 at 01:07:39PM +0200, Krzysztof Kozlowski wrote:
> On Fri, 31 Aug 2018 at 09:39, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote:
> >
> > Hi Krzysztof,
> >
> > Some comments inline.
> >
> > On Thu, Aug 30, 2018 at 07:15:39PM +0200, Krzysztof Kozlowski wrote:
> > > Add driver for using the Freescale/NXP Vybrid processor CRC block for
> > > CRC16 and CRC32 offloading. The driver implements shash_alg and was
> > > tested using internal testmgr tests and libkcapi.
> > >
> > > Signed-off-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> > > ---
> > > MAINTAINERS | 7 +
> > > drivers/crypto/Kconfig | 10 ++
> > > drivers/crypto/Makefile | 1 +
> > > drivers/crypto/vf-crc.c | 387 ++++++++++++++++++++++++++++++++++++++++++++++
> > > include/linux/crc32poly.h | 7 +
> > > 5 files changed, 412 insertions(+)
> > > create mode 100644 drivers/crypto/vf-crc.c
> > >
> > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > index 0a340f680230..e84fa829a4e4 100644
> > > --- a/MAINTAINERS
> > > +++ b/MAINTAINERS
> > > @@ -15388,6 +15388,13 @@ S: Maintained
> > > F: Documentation/fb/uvesafb.txt
> > > F: drivers/video/fbdev/uvesafb.*
> > >
> > > +VF500/VF610 HW CRC DRIVER
> > > +M: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> > > +L: linux-crypto@xxxxxxxxxxxxxxx
> > > +S: Maintained
> > > +F: drivers/crypto/vf-crc.c
> > > +F: Documentation/devicetree/bindings/crypto/fsl-vf610-crc.txt
> > > +
> > > VF610 NAND DRIVER
> > > M: Stefan Agner <stefan@xxxxxxxx>
> > > L: linux-mtd@xxxxxxxxxxxxxxxxxxx
> > > diff --git a/drivers/crypto/Kconfig b/drivers/crypto/Kconfig
> > > index 20314d7a7b58..0ade940ac79c 100644
> > > --- a/drivers/crypto/Kconfig
> > > +++ b/drivers/crypto/Kconfig
> > > @@ -418,6 +418,16 @@ config CRYPTO_DEV_MXS_DCP
> > > To compile this driver as a module, choose M here: the module
> > > will be called mxs-dcp.
> > >
> > > +config CRYPTO_DEV_VF_CRC
> > > + tristate "Support for Freescale/NXP Vybrid CRC HW accelerator"
> > > + select CRYPTO_HASH
> > > + help
> > > + This option enables support for the CRC16/32 hardware accelerator
> > > + on Freescale/NXP Vybrid VF500/VF610 SoCs.
> > > +
> > > + To compile this driver as a module, choose M here: the module
> > > + will be called vf-crc.
> > > +
> > > config CRYPTO_DEV_EXYNOS_RNG
> > > tristate "EXYNOS HW pseudo random number generator support"
> > > depends on ARCH_EXYNOS || COMPILE_TEST
> > > diff --git a/drivers/crypto/Makefile b/drivers/crypto/Makefile
> > > index c23396f32c8a..418c08bdc19c 100644
> > > --- a/drivers/crypto/Makefile
> > > +++ b/drivers/crypto/Makefile
> > > @@ -41,6 +41,7 @@ obj-$(CONFIG_ARCH_STM32) += stm32/
> > > obj-$(CONFIG_CRYPTO_DEV_SUN4I_SS) += sunxi-ss/
> > > obj-$(CONFIG_CRYPTO_DEV_TALITOS) += talitos.o
> > > obj-$(CONFIG_CRYPTO_DEV_UX500) += ux500/
> > > +obj-$(CONFIG_CRYPTO_DEV_VF_CRC) += vf-crc.o
> > > obj-$(CONFIG_CRYPTO_DEV_VIRTIO) += virtio/
> > > obj-$(CONFIG_CRYPTO_DEV_VMX) += vmx/
> > > obj-$(CONFIG_CRYPTO_DEV_BCM_SPU) += bcm/
> > > +static int vf_crc_update_prepare(struct vf_crc_tfm_ctx *mctx,
> > > + struct vf_crc_desc_ctx *desc_ctx)
> > > +{
> > > + struct vf_crc *crc = desc_ctx->crc;
> > > + int ret;
> > > +
> > > + ret = clk_prepare_enable(crc->clk);
> > > + if (ret) {
> > > + dev_err(crc->dev, "Failed to enable clock\n");
> > > + return ret;
> > > + }
> >
> > Generally have you measured the performance of this driver? Is it faster
> > than the software implementation?
>
> I wanted to replace our in-house out-of-tree, hacky ioctl-based driver
> with something more upstreamable. I run few simple user-space
> performance tests and in fact SW implementation is faster. Around 5x
> faster for this version of driver. However it depends highly on size
> of message (buffer) because there is big overhead of libkcapi.
Well, I meant comparing the hardware vs. software implementation directly
in the kernel. Of course when a userspace API is involved the comparison
is not fair.
>
> The typical SW implementation (with lookup tables) is just fetching of
> data from memory and computing. Usage of libkcapi is at least three
> library function calls on user-space side and a bunch of other code on
> kernel side.
>
> There are two benefits:
> 1. CPU could be offloaded and do something in parallel. However for
> this I should probably implement asymmetric hash. Otherwise wastes
> cycles on reading from CRC registers... and of course on clk prepare
> and mutex handing.
The CPU can only do something in parallel when it's otherwise idle. In
your driver the CPU is 100% busy, so no time to do something else.
> 2. Theoretically it could lower energy consumption... as CPU would not
> be that busy. I found 3% lower power usage (0.18 A -> 0.175 A) but if
> you multiply it per time then total energy spent would be higher.
>
> Does this driver makes sense in such case? In fact I have doubts...
>
> It was nice exercise for me though. :)
>
> >
> > Under certain circumstances a clk_prepare_enable might become expensive,
> > so it could happen that all this clk enabling/disabling takes longer
> > than the action you do in between. Using pm_runtime might help here.
>
> I should convert them to just clk_enable/disable. The pm_runtime is
> also a huge framework and adds its own overhead. Using it just to
> toggle one clock is a lot.
There are probably more drivers in your system that make use of
pm_runtime, so no need to add it only for this one driver.
Sascha
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