From: Nicolin Chen <nicolinc@nvidia.com>
To: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Cc: Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
"Joerg Roedel" <joro@8bytes.org>,
Jason Gunthorpe <jgg@nvidia.com>,
"Pranjal Shrivastava" <praan@google.com>,
Mostafa Saleh <smostafa@google.com>,
"Thierry Reding" <thierry.reding@kernel.org>,
Krishna Reddy <vdumpa@nvidia.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Breno Leitao <leitao@debian.org>, Kyle McMartin <jkkm@meta.com>,
Usama Arif <usama.arif@linux.dev>, <kernel-team@meta.com>,
<linux-arm-kernel@lists.infradead.org>, <iommu@lists.linux.dev>,
<linux-tegra@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 1/2] iommu/arm-smmu-v3: Add a cmdq_entries module parameter
Date: Wed, 2 Sep 2026 10:22:31 -0700 [thread overview]
Message-ID: <aphbV1FSoop1YGOQ@nvidia.com> (raw)
In-Reply-To: <20260902121724.3494954-2-kas@kernel.org>
On Wed, Sep 02, 2026 at 01:17:23PM +0100, Kiryl Shutsemau (Meta) wrote:
> +/**
> + * arm_smmu_queue_max_n_shift() - pick the log2 depth of a queue
> + * @hw_shift: log2 depth the hardware allows, capped for natural alignment
> + * @ent_sz_shift: log2 of the queue entry size in bytes
> + * @want: number of entries asked for, or zero to use @hw_shift
> + *
> + * @want is rounded down to a power of two. It never sizes a queue below one
> + * page, because coherent DMA is page granular: a shallower queue occupies the
> + * same memory as one that fills the page, and arm_smmu_init_one_queue() stops
> + * shrinking at a page too.
Well, since we want the cmdq depth, why not name the parameter
"max_cmdq_depth"? Then, no rounding and more straightforward.
Nicolin
next prev parent reply other threads:[~2026-09-02 17:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-02 12:17 [PATCH v4 0/2] iommu/arm-smmu-v3: Make the queue depths tunable, and shrink them in a kdump kernel Kiryl Shutsemau (Meta)
2026-09-02 12:17 ` [PATCH v4 1/2] iommu/arm-smmu-v3: Add a cmdq_entries module parameter Kiryl Shutsemau (Meta)
2026-09-02 17:22 ` Nicolin Chen [this message]
2026-09-03 14:15 ` Kiryl Shutsemau
2026-09-03 15:09 ` Nicolin Chen
2026-09-04 14:28 ` Kiryl Shutsemau
2026-09-02 12:17 ` [PATCH v4 2/2] iommu/arm-smmu-v3: Default queue depths to one page in a kdump kernel Kiryl Shutsemau (Meta)
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