Re: [PATCH 1/2] Revert "iommu/amd: Fix performance counter initialization"

[Suthikulpanit, Suravee]

Shuah,

On 4/10/2021 12:06 AM, Shuah Khan wrote:
> > diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> > index 321f5906e6ed..648cdfd03074 100644
> > --- a/drivers/iommu/amd/init.c
> > +++ b/drivers/iommu/amd/init.c
> > ....
> > @@ -1729,39 +1728,17 @@ static void __init init_iommu_perf_ctr(struct amd_iommu *iommu)
> >       amd_iommu_pc_present = true;
> >       /* save the value to restore, if writable */
> > -    if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false) ||
> > -        iommu_pc_get_set_reg(iommu, 0, 0, 8, &save_src, false))
> > -        goto pc_false;
> > -
> > -    /*
> > -     * Disable power gating by programing the performance counter
> > -     * source to 20 (i.e. counts the reads and writes from/to IOMMU
> > -     * Reserved Register [MMIO Offset 1FF8h] that are ignored.),
> > -     * which never get incremented during this init phase.
> > -     * (Note: The event is also deprecated.)
> > -     */
> > -    val = 20;
> > -    if (iommu_pc_get_set_reg(iommu, 0, 0, 8, &val, true))
> > +    if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false))
> >           goto pc_false;
> >       /* Check if the performance counters can be written to */
> > -    val = 0xabcd;
> > -    for (retry = 5; retry; retry--) {
> > -        if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true) ||
> > -            iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false) ||
> > -            val2)
> > -            break;
> > -
> > -        /* Wait about 20 msec for power gating to disable and retry. */
> > -        msleep(20);
> > -    }
> > -
> > -    /* restore */
> > -    if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, true) ||
> > -        iommu_pc_get_set_reg(iommu, 0, 0, 8, &save_src, true))
> > +    if ((iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true)) ||
> > +        (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false)) ||
> > +        (val != val2))
>
> Probably don't need parentheses around 'val != val2'

This is the result from git revert. Also, the logic is removed in patch 2/2.

Suravee