Re: [PATCH v7 6/7] iommu/riscv: Command and fault queue support

[Andrew Jones]

On Wed, Jun 05, 2024 at 12:57:48PM GMT, Tomasz Jeznach wrote:
...
> +static int riscv_iommu_queue_alloc(struct riscv_iommu_device *iommu,
> +				   struct riscv_iommu_queue *queue,
> +				   size_t entry_size)
> +{
> +	unsigned int logsz;
> +	u64 qb, rb;
> +
> +	/*
> +	 * Use WARL base register property to discover maximum allowed
> +	 * number of entries and optional fixed IO address for queue location.
> +	 */
> +	riscv_iommu_writeq(iommu, queue->qbr, RISCV_IOMMU_QUEUE_LOG2SZ_FIELD);
> +	qb = riscv_iommu_readq(iommu, queue->qbr);
> +
> +	/*
> +	 * Calculate and verify hardware supported queue length, as reported
> +	 * by the field LOG2SZ, where max queue length is equal to 2^(LOG2SZ + 1).
> +	 * Update queue size based on hardware supported value.
> +	 */
> +	logsz = ilog2(queue->mask);
> +	if (logsz > FIELD_GET(RISCV_IOMMU_QUEUE_LOG2SZ_FIELD, qb))
> +		logsz = FIELD_GET(RISCV_IOMMU_QUEUE_LOG2SZ_FIELD, qb);
> +
> +	/*
> +	 * Use WARL base register property to discover an optional fixed IO
> +	 * address for queue ring buffer location. Otherwise allocate contiguous
> +	 * system memory.
> +	 */
> +	if (FIELD_GET(RISCV_IOMMU_PPN_FIELD, qb)) {
> +		const size_t queue_size = entry_size << (logsz + 1);
> +
> +		queue->phys = ppn_to_phys(FIELD_GET(RISCV_IOMMU_PPN_FIELD, qb));

Shouldn't this be something like

  FIELD_GET(RISCV_IOMMU_PPN_FIELD, qb) << PAGE_SHIFT

ppn_to_phys() assumes the ppn it's converting to be shifted up by 10, but
FIELD_GET has shifted it down to zero.

Thanks,
drew