[PATCH v5 05/27] iommu/arm-smmu-v3: Make CD programming use arm_smmu_write_entry()

[Jason Gunthorpe]

On Sat, Mar 23, 2024 at 01:02:15PM +0000, Mostafa Saleh wrote:
> > +static void arm_smmu_get_cd_used(const __le64 *ent, __le64 *used_bits)
> > +{
> > +	used_bits[0] = cpu_to_le64(CTXDESC_CD_0_V);
> > +	if (!(ent[0] & cpu_to_le64(CTXDESC_CD_0_V)))
> > +		return;
> > +	memset(used_bits, 0xFF, sizeof(struct arm_smmu_cd));
> 
> This is a slightly different approach than what the driver does for STEs,
> where it explicitly sets the used bits. Is there a reason for that?

It is just more compact this way

> > +	/* EPD0 means T0SZ/TG0/IR0/OR0/SH0/TTB0 are IGNORED */
> > +	if (ent[0] & cpu_to_le64(CTXDESC_CD_0_TCR_EPD0)) {
> > +		used_bits[0] &= ~cpu_to_le64(
> > +			CTXDESC_CD_0_TCR_T0SZ | CTXDESC_CD_0_TCR_TG0 |
> > +			CTXDESC_CD_0_TCR_IRGN0 | CTXDESC_CD_0_TCR_ORGN0 |
> > +			CTXDESC_CD_0_TCR_SH0);
> > +		used_bits[1] &= ~cpu_to_le64(CTXDESC_CD_1_TTB0_MASK);
> > +	}
> > +}
> 
> We should add a comment about EPD1 maybe?

Driver doesn't use TTB1?

Jason