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

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Message-ID: <a661f86c-7ecc-46fc-a3af-90ad05a0c603@quicinc.com>
Date: Mon, 24 Mar 2025 16:29:49 +0800
From: Baochen Qiang <quic_bqiang@...cinc.com>
To: Johan Hovold <johan@...nel.org>
CC: Johan Hovold <johan+linaro@...nel.org>,
        Jeff Johnson
	<jjohnson@...nel.org>,
        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 3/24/2025 4:20 PM, Johan Hovold wrote:
> On Mon, Mar 24, 2025 at 04:05:33PM +0800, Baochen Qiang wrote:
>> On 3/24/2025 3:40 PM, Johan Hovold wrote:
>>> On Mon, Mar 24, 2025 at 11:06:16AM +0800, Baochen Qiang wrote:
>>>> 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.
>>>>
>>>> could you help elaborate how it could be extended?
>>>
>>> The mask should reflect the capability of the device. That may be
>>> 64 (or 40) bits, but I've only been able to test using 36 bits.
>>
>> are you talking about QCN9274? As far as I know, WCN7850 does not support 40 bits or more.
> 
> Or really all devices handled by ath12k since they at least currently
> use a common mask.
> 
> The T14s has a:
> 
> 	0004:01:00.0 Network controller: Qualcomm Technologies, Inc WCN785x Wi-Fi 7(802.11be) 320MHz 2x2 [FastConnect 7800] (rev 01)
> 
> 	ath12k_pci 0004:01:00.0: Hardware name: wcn7850 hw2.0
> 	ath12k_pci 0004:01:00.0: chip_id 0x2 chip_family 0x4 board_id 0xff soc_id 0x40170200
> 
> Sounds like 36 bits is the correct choice for now then.

yes, let's keep it as 36 for now.

> 
> Johan