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

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Date: Mon, 10 Jun 2024 13:06:09 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Tomasz Jeznach <tjeznach@...osinc.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Anup Patel <apatel@...tanamicro.com>, Sunil V L <sunilvl@...tanamicro.com>, 
	Nick Kossifidis <mick@....forth.gr>, Sebastien Boeuf <seb@...osinc.com>, 
	Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org, iommu@...ts.linux.dev, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, linux@...osinc.com, 
	Lu Baolu <baolu.lu@...ux.intel.com>, Zong Li <zong.li@...ive.com>
Subject: Re: [PATCH v7 6/7] iommu/riscv: Command and fault queue support

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