On Tue, Jun 23, 2020 at 03:19:41PM -0700, Manasi Navare wrote:
> On Tue, Jun 23, 2020 at 11:50:27PM +0300, Imre Deak wrote:
> > On Tue, Jun 23, 2020 at 01:32:50PM -0700, Manasi Navare wrote:
> >
> > with two functions it would get:
> >
> > intel_ddi_wait_for_ddi_buf_active(i915, port)
> > {
> > if (GEN <= 9) {
> > usleep_range(600, 1000);
>
> The doumentation however does suggest that we use udelay to avoid the overhead
> of setting up hrtimers needed for usleep_range in atomic context.
The relevant part here is "NON-ATOMIC CONTEXT":
SLEEPING FOR "A FEW" USECS ( < ~10us? ):
* Use udelay
- Why not usleep?
On slower systems, (embedded, OR perhaps a speed-
stepped PC!) the overhead of setting up the hrtimers
for usleep *may* not be worth it. Such an evaluation
will obviously depend on your specific situation, but
it is something to be aware of.
SLEEPING FOR ~USECS OR SMALL MSECS ( 10us - 20ms):
* Use usleep_range
So, can use udelay() for 16usec and should use usleep_range() for 600 usec.
> But then checkpatch also suggests using usleep_range, why is that?
>
> so still not clear in the context of i915 how we decide where to use jiffie based
> delay through udelay and when to use hrtimers (usleep)?
The above document should be followed.
>
> Manasi
>
>
> > return;
> > }
> >
> > if (wait_for_us(!(read(BUF_CTL) & IS_IDLE), 600))
> > drm_err("Port %c: Timeout waiting for DDI BUF to get active\n", port));
> > }
> >
> > intel_ddi_wait_for_ddi_buf_idle(i915, port)
> > {
> > if (BXT) {
> > udelay(16);
> > return;
> > }
> >
> > if (wait_for_us(read(BUF_CTL) & IS_IDLE, 600))
> > drm_err("Port %c: Timeout waiting for DDI BUF to get idle\n", port));
> > }
> >
> > --Imre
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