linux-kernel - Re: [PATCH] wifi: ath12k: extend dma mask to 36 bits

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Message-ID: <0e2060ec-f0ed-41dc-8325-0ec839a59dd5@quicinc.com>
Date: Mon, 24 Mar 2025 16:33:13 +0800
From: Baochen Qiang <quic_bqiang@...cinc.com>
To: Johan Hovold <johan+linaro@...nel.org>, Jeff Johnson <jjohnson@...nel.org>
CC: Stephan Gerhold <stephan.gerhold@...aro.org>, <ath12k@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] wifi: ath12k: extend dma mask to 36 bits



On 3/22/2025 12:23 AM, Johan Hovold wrote:
> Extend the DMA mask to 36 bits to avoid using bounce buffers on machines
> without an iommu (under OS control) similar to what was done for ath11k
> in commit dbd73acb22d8 ("wifi: ath11k: enable 36 bit mask for stream
> DMA").
> 
> This specifically avoids using bounce buffers on Qualcomm Snapdragon X
> Elite machines like the Lenovo ThinkPad T14s when running at EL1.
> 
> Note that the mask could possibly be extended further but unresolved DMA
> issues with 64 GiB X Elite machines currently prevents that from being
> tested.
> 
> Also note that the driver is limited to 32 bits for coherent
> allocations and that there is no need to check for errors when setting
> masks larger than 32 bits.
> 
> Tested-on: WCN7850 hw2.0 WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
> 
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>  drivers/net/wireless/ath/ath12k/mhi.c |  2 +-
>  drivers/net/wireless/ath/ath12k/pci.c | 12 ++++--------
>  drivers/net/wireless/ath/ath12k/pci.h |  1 +
>  3 files changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath12k/mhi.c b/drivers/net/wireless/ath/ath12k/mhi.c
> index 2f6d14382ed7..9c929c4ad8a8 100644
> --- a/drivers/net/wireless/ath/ath12k/mhi.c
> +++ b/drivers/net/wireless/ath/ath12k/mhi.c
> @@ -379,7 +379,7 @@ int ath12k_mhi_register(struct ath12k_pci *ab_pci)
>  		mhi_ctrl->irq_flags = IRQF_SHARED | IRQF_NOBALANCING;
>  
>  	mhi_ctrl->iova_start = 0;
> -	mhi_ctrl->iova_stop = 0xffffffff;
> +	mhi_ctrl->iova_stop = ab_pci->dma_mask;
>  	mhi_ctrl->sbl_size = SZ_512K;
>  	mhi_ctrl->seg_len = SZ_512K;
>  	mhi_ctrl->fbc_download = true;
> diff --git a/drivers/net/wireless/ath/ath12k/pci.c b/drivers/net/wireless/ath/ath12k/pci.c
> index 06cff3849ab8..e77c50fc48ca 100644
> --- a/drivers/net/wireless/ath/ath12k/pci.c
> +++ b/drivers/net/wireless/ath/ath12k/pci.c
> @@ -17,7 +17,7 @@
>  #include "debug.h"
>  
>  #define ATH12K_PCI_BAR_NUM		0
> -#define ATH12K_PCI_DMA_MASK		32
> +#define ATH12K_PCI_DMA_MASK		36
>  
>  #define ATH12K_PCI_IRQ_CE0_OFFSET		3
>  
> @@ -874,13 +874,9 @@ static int ath12k_pci_claim(struct ath12k_pci *ab_pci, struct pci_dev *pdev)
>  		goto disable_device;
>  	}
>  
> -	ret = dma_set_mask_and_coherent(&pdev->dev,
> -					DMA_BIT_MASK(ATH12K_PCI_DMA_MASK));
> -	if (ret) {
> -		ath12k_err(ab, "failed to set pci dma mask to %d: %d\n",
> -			   ATH12K_PCI_DMA_MASK, ret);
> -		goto release_region;
> -	}
> +	ab_pci->dma_mask = DMA_BIT_MASK(ATH12K_PCI_DMA_MASK);
> +	dma_set_mask(&pdev->dev, ab_pci->dma_mask);
> +	dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32));
>  
>  	pci_set_master(pdev);
>  
> diff --git a/drivers/net/wireless/ath/ath12k/pci.h b/drivers/net/wireless/ath/ath12k/pci.h
> index 31584a7ad80e..9e89b64b3545 100644
> --- a/drivers/net/wireless/ath/ath12k/pci.h
> +++ b/drivers/net/wireless/ath/ath12k/pci.h
> @@ -116,6 +116,7 @@ struct ath12k_pci {
>  	unsigned long irq_flags;
>  	const struct ath12k_pci_ops *pci_ops;
>  	u32 qmi_instance;
> +	u64 dma_mask;
>  };
>  
>  static inline struct ath12k_pci *ath12k_pci_priv(struct ath12k_base *ab)

Reviewed-by: Baochen Qiang <quic_bqiang@...cinc.com>

With WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3 this is working, so:

Tested-by: Baochen Qiang <quic_bqiang@...cinc.com>