linux-kernel - Re: [PATCH RFC] staging: r8188eu: comment about the chip's packet format

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Date:   Fri, 18 Feb 2022 11:45:31 -0600
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Martin Kaiser <martin@...ser.cx>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Michael Straube <straube.linux@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] staging: r8188eu: comment about the chip's packet
 format

On 2/18/22 04:22, Dan Carpenter wrote:
> On Fri, Feb 18, 2022 at 10:22:53AM +0100, Martin Kaiser wrote:
>> The structs phy_rx_agc_info and phy_status_rpt define parts of the
>> header data that the r8188eu chipset sends to this driver via usb.
>>
>> Add a comment to clarify that we cannot modify the content of these
>> structures and remove seemingly unused fields.
>>
>> Signed-off-by: Martin Kaiser <martin@...ser.cx>
>> ---
>>
>> Dear all,
>>
>> I experimented with "cleaning up" these structures and related code before
>> discovering that their content comes from usb packets we receive from the
>> r8188eu chipset.
>>
>> Would it make sense to add a word of warning to prevent others from
>> repeating this exercise?
> 
> Just the fact that these structs are endian means they're from the
> firmware or the network.
> 
> If a struct has a pointer in it, then it's rarely part of the UAPI but
> if it has endian data then it probably is.

Additionally, do not change any struct with the __packed attribute. Most will 
have endian variables as well, but not all will.

Testing after modifying any struct is a necessity.

Larry