> -----Original Message-----
> From: Antoine Tenart <antoine.tenart@xxxxxxxxxxx>
> Sent: Monday, August 5, 2019 11:54 AM
> To: Pascal Van Leeuwen <pvanleeuwen@xxxxxxxxxxxxxx>
> Cc: Antoine Tenart <antoine.tenart@xxxxxxxxxxx>; Pascal van Leeuwen
> <pascalvanl@xxxxxxxxx>; linux-crypto@xxxxxxxxxxxxxxx; herbert@xxxxxxxxxxxxxxxxxxx;
> davem@xxxxxxxxxxxxx
> Subject: Re: [PATCHv3 4/4] crypto: inside-secure - add support for using the EIP197
> without vendor firmware
>
> On Mon, Aug 05, 2019 at 09:48:13AM +0000, Pascal Van Leeuwen wrote:
> > > On Wed, Jul 31, 2019 at 05:29:19PM +0200, Pascal van Leeuwen wrote:
> > > >
> > > > - /* Release engine from reset */
> > > > - val = readl(EIP197_PE(priv) + ctrl);
> > > > - val &= ~EIP197_PE_ICE_x_CTRL_SW_RESET;
> > > > - writel(val, EIP197_PE(priv) + ctrl);
> > > > + for (pe = 0; pe < priv->config.pes; pe++) {
> > > > + base = EIP197_PE_ICE_SCRATCH_RAM(pe);
> > > > + pollcnt = EIP197_FW_START_POLLCNT;
> > > > + while (pollcnt &&
> > > > + (readl_relaxed(EIP197_PE(priv) + base +
> > > > + pollofs) != 1)) {
> > > > + pollcnt--;
> > >
> > > You might want to use readl_relaxed_poll_timeout() here, instead of a
> > > busy polling.
> > >
> > Didn't know such a thing existed, but I also wonder how appropriate it
> > is in this case, condering it measures in whole microseconds, while the
> > response time I'm expecting here is in the order of a few dozen nano-
> > seconds internally ... i.e. 1 microsecond is already a *huge* overkill.
> >
> > The current implementation runs that loop for only 16 iterations which
> > should be both more than sufficient (it probably could be reduced
> > further, I picked 16 rather arbitrarily) and at the same time take so
> > few cycles on the CPU that I doubt it is worthwhile to reschedule/
> > preempt/whatever?
>
> Your choice, I was just making a suggestion :)
>
And I appreciate that, as I now know about this
readl_relaxed_poll_timeout() which I'm sure I will need for something
someday. I was just asking for comments on this particular situation.
After reading the implementation code, I think using it with a
sleep_us value of 0 and a time-out value of 1 may be reasonable here,
as time-out means some serious error that shouldn't normally happen.
I just wouldn't want any microsecond delays for the "normal" case.
> Thanks,
> Antoine
>
> --
> Antoine Ténart, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
Regards,
Pascal van Leeuwen
Silicon IP Architect, Multi-Protocol Engines @ Verimatrix
www.insidesecure.com
