linux-kernel - Re: [PATCH] dmaengine: apple-admac: Avoid accessing registers in probe

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Message-ID: <Z03f08Os/csGbMap@vaman>
Date: Mon, 2 Dec 2024 21:56:59 +0530
From: Vinod Koul <vkoul@...nel.org>
To: fnkl.kernel@...il.com
Cc: Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
	Alyssa Rosenzweig <alyssa@...enzweig.io>,
	Martin Povišer <povik+lin@...ebit.org>,
	asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: apple-admac: Avoid accessing registers in
 probe

On 24-11-24, 16:48, Sasha Finkelstein via B4 Relay wrote:
> From: Sasha Finkelstein <fnkl.kernel@...il.com>
> 
> The ADMAC attached to the AOP has complex power sequencing, and is
> power gated when the probe callback runs. Move the register reads
> to other functions, where we can guarantee that the hardware is
> switched on.

So looking at the driver, there is code to turn power, so what ensures
that power is up while we are in alloc callback

> 
> Fixes: 568aa6dd641f ("dmaengine: apple-admac: Allocate cache SRAM to channels")
> Signed-off-by: Sasha Finkelstein <fnkl.kernel@...il.com>
> ---
>  drivers/dma/apple-admac.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/apple-admac.c b/drivers/dma/apple-admac.c
> index 9588773dd2eb670a2f6115fdaef39a0e88248015..037ec38730cf980eee11ebb8ec17be7623879cf8 100644
> --- a/drivers/dma/apple-admac.c
> +++ b/drivers/dma/apple-admac.c
> @@ -153,6 +153,8 @@ static int admac_alloc_sram_carveout(struct admac_data *ad,
>  {
>  	struct admac_sram *sram;
>  	int i, ret = 0, nblocks;

Empty line before this please

> +	ad->txcache.size = readl_relaxed(ad->base + REG_TX_SRAM_SIZE);
> +	ad->rxcache.size = readl_relaxed(ad->base + REG_RX_SRAM_SIZE);
>  
>  	if (dir == DMA_MEM_TO_DEV)
>  		sram = &ad->txcache;
> @@ -912,12 +914,7 @@ static int admac_probe(struct platform_device *pdev)
>  		goto free_irq;
>  	}
>  
> -	ad->txcache.size = readl_relaxed(ad->base + REG_TX_SRAM_SIZE);
> -	ad->rxcache.size = readl_relaxed(ad->base + REG_RX_SRAM_SIZE);
> -
>  	dev_info(&pdev->dev, "Audio DMA Controller\n");
> -	dev_info(&pdev->dev, "imprint %x TX cache %u RX cache %u\n",
> -		 readl_relaxed(ad->base + REG_IMPRINT), ad->txcache.size, ad->rxcache.size);
>  
>  	return 0;
>  
> 
> ---
> base-commit: 9f16d5e6f220661f73b36a4be1b21575651d8833
> change-id: 20241124-admac-power-7f32c2a1850a
> 

-- 
~Vinod