linux-kernel - Re: [PATCH v8 3/5] iommu/arm-smmu: introduction of ACTLR for custom prefetcher settings

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Date: Thu, 18 Jan 2024 18:55:29 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Bibek Kumar Patro <quic_bibekkum@...cinc.com>, will@...nel.org,
 robin.murphy@....com, joro@...tes.org, dmitry.baryshkov@...aro.org,
 jsnitsel@...hat.com, quic_bjorande@...cinc.com, mani@...nel.org,
 quic_eberman@...cinc.com, robdclark@...omium.org,
 u.kleine-koenig@...gutronix.de, robh@...nel.org, vladimir.oltean@....com,
 quic_pkondeti@...cinc.com, quic_molvera@...cinc.com
Cc: linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 3/5] iommu/arm-smmu: introduction of ACTLR for custom
 prefetcher settings



On 1/16/24 16:04, Bibek Kumar Patro wrote:
> Currently in Qualcomm  SoCs the default prefetch is set to 1 which allows
> the TLB to fetch just the next page table. MMU-500 features ACTLR
> register which is implementation defined and is used for Qualcomm SoCs
> to have a custom prefetch setting enabling TLB to prefetch the next set
> of page tables accordingly allowing for faster translations.
> 
> ACTLR value is unique for each SMR (Stream matching register) and stored
> in a pre-populated table. This value is set to the register during
> context bank initialisation.
> 
> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

Since it's your idea with Dmitry's review suggestions, I don't think
this tag makes sense.

It's normally used for situations like:

Colleague X: "Hey Bibek, I noticed x broke on y, can you fix it?"
"Sure!" <proceeds to make a commit with suggested-by Colleague X>

Just a nit below:

> +struct actlr_config {
> +	u16 sid;
> +	u16 mask;
> +	u32 actlr;
> +};

This, can go here, in the header:

> +struct actlr_config;
> +
> +struct actlr_variant {
> +	const resource_size_t io_start;
> +	const struct actlr_config * const actlrcfg;
> +	const size_t num_actlrcfg;
> +};
> +

Otherwise, this looks good!

Konrad