netdev - Re: [PATCH 02/13] wifi: nl80211: send underlying multi-hardware channel capabilities to user space

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Message-ID: <b455f267-9552-be3b-95b0-a036bfa8e14a@quicinc.com>
Date: Fri, 29 Mar 2024 19:51:26 +0530
From: Vasanthakumar Thiagarajan <quic_vthiagar@...cinc.com>
To: Johannes Berg <johannes@...solutions.net>,
        Karthikeyan Periyasamy
	<quic_periyasa@...cinc.com>,
        <ath12k@...ts.infradead.org>
CC: <linux-wireless@...r.kernel.org>, <netdev@...r.kernel.org>,
        Jakub Kicinski
	<kuba@...nel.org>
Subject: Re: [PATCH 02/13] wifi: nl80211: send underlying multi-hardware
 channel capabilities to user space



On 3/28/2024 5:31 PM, Johannes Berg wrote:
> On Thu, 2024-03-28 at 15:48 +0530, Karthikeyan Periyasamy wrote:
>> On 3/28/2024 1:19 PM, Johannes Berg wrote:
>>> On Thu, 2024-03-28 at 12:59 +0530, Karthikeyan Periyasamy wrote:
>>>> +/**
>>>> + * nl80211_multi_hw_attrs - multi-hw attributes
>>>> + *
>>>> + * @NL80211_MULTI_HW_ATTR_INVALID: invalid
>>>> + * @NL80211_MULTI_HW_ATTR_IDX: (u8) multi-HW index to refer the underlying HW
>>>> + *	for which the supported channel list is advertised. Internally refer
>>>> + *	the index of the wiphy's @hw_chans array.
>>> Is there a good reason to expose this? Seems pretty internal to me, and
>>> not sure what userspace would do with it?
>>
>> Hostapd use this hw index for the channel switch cmd.
> 
> What, where? I don't see that in this patchset? And why??
> 
> In any case, unless I just missed it and you're going to tell me to look
> at patch N, we don't need it here, and then I'd prefer to keep it an
> internal detail until it's needed.
> 
>> The hw index used as a sanity check to identify whether the user
>> requested channel fall under the different hw or not.
> 
> You mean within hostapd itself? That doesn't make sense, it can derive
> that information differently.
> 
>> In split-phy hardware, 5GHz band supported by two physical hardware's.
>> First supports 5GHz Low band and second supports 5GHz High band.
> 
> In your hardware design anyway, but yeah, I get it.
> 
>> In this case, user space cannot use band vise check here to identify
>> given channel or freq supported in the given hardware.
> 
> No, but it also doesn't need an index assigned by the kernel for that.
> 

The only purpose of hw index is to link hw_chans to per-hardware 
interface combination capability so that each hardware can be
identified during interface combination checks capability vs
current state. Thinking if we can embed the channel list also
into per-hardware interface combination signaling by giving the
pointer?

Vasanth