linux-kernel - Re: [PATCH 2/5] iommu/dart: Skip reset for locked DARTs

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Message-ID: <98af5c02-5006-4272-aaf0-a0e30c312059@arm.com>
Date: Tue, 11 Feb 2025 18:34:27 +0000
From: Robin Murphy <robin.murphy@....com>
To: Alyssa Rosenzweig <alyssa@...enzweig.io>, Sven Peter
 <sven@...npeter.dev>, Janne Grunau <j@...nau.net>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>
Cc: asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Hector Martin <marcan@...can.st>
Subject: Re: [PATCH 2/5] iommu/dart: Skip reset for locked DARTs

On 2025-02-10 7:39 pm, Alyssa Rosenzweig wrote:
> Locked DARTs cannot be reconfigured, therefore the reset/restore
> procedure can't work and should not be needed. Skip it, allowing locked
> DARTs to probe.
> 
> Co-developed-by: Hector Martin <marcan@...can.st>
> Signed-off-by: Hector Martin <marcan@...can.st>
> Signed-off-by: Alyssa Rosenzweig <alyssa@...enzweig.io>
> ---
>   drivers/iommu/apple-dart.c | 24 ++++++++++++------------
>   1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c
> index 460cf96bc8001e051916f356d5d175b35e36c608..9c74a95eb7e819e94ab2fb47ed0d411a1eba8bf7 100644
> --- a/drivers/iommu/apple-dart.c
> +++ b/drivers/iommu/apple-dart.c
> @@ -452,17 +452,9 @@ apple_dart_t8110_hw_invalidate_tlb(struct apple_dart_stream_map *stream_map)
>   
>   static int apple_dart_hw_reset(struct apple_dart *dart)
>   {
> -	u32 config;
>   	struct apple_dart_stream_map stream_map;
>   	int i;
>   
> -	config = readl(dart->regs + dart->hw->lock);
> -	if (config & dart->hw->lock_bit) {
> -		dev_err(dart->dev, "DART is locked down until reboot: %08x\n",
> -			config);
> -		return -EINVAL;
> -	}
> -
>   	stream_map.dart = dart;
>   	bitmap_zero(stream_map.sidmap, DART_MAX_STREAMS);
>   	bitmap_set(stream_map.sidmap, 0, dart->num_streams);
> @@ -1151,9 +1143,11 @@ static int apple_dart_probe(struct platform_device *pdev)
>   	}
>   
>   	dart->locked = apple_dart_is_locked(dart);
> -	ret = apple_dart_hw_reset(dart);
> -	if (ret)
> -		goto err_clk_disable;
> +	if (!dart->locked) {
> +		ret = apple_dart_hw_reset(dart);
> +		if (ret)
> +			goto err_clk_disable;
> +	}
>   
>   	ret = request_irq(dart->irq, dart->hw->irq_handler, IRQF_SHARED,
>   			  "apple-dart fault handler", dart);
> @@ -1192,7 +1186,9 @@ static void apple_dart_remove(struct platform_device *pdev)
>   {
>   	struct apple_dart *dart = platform_get_drvdata(pdev);
>   
> -	apple_dart_hw_reset(dart);
> +	if (!dart->locked)
> +		apple_dart_hw_reset(dart);

Not much point saving anything on suspend either, in that case.

Thanks,
Robin.

> +
>   	free_irq(dart->irq, dart);
>   
>   	iommu_device_unregister(&dart->iommu);
> @@ -1325,6 +1321,10 @@ static __maybe_unused int apple_dart_resume(struct device *dev)
>   	unsigned int sid, idx;
>   	int ret;
>   
> +	/* Locked DARTs can't be restored, and they should not need it */
> +	if (dart->locked)
> +		return 0;
> +
>   	ret = apple_dart_hw_reset(dart);
>   	if (ret) {
>   		dev_err(dev, "Failed to reset DART on resume\n");
>