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Date: Thu, 1 Feb 2024 11:14:47 +0530
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Subject: Re: [PATCH v2] usb: gadget: ncm: Avoid dropping datagrams of properly
 parsed NTBs
To: =?UTF-8?Q?Maciej_=C5=BBenczykowski?= <maze@google.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hardik Gajjar
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From: Krishna Kurapati PSSNV <quic_kriskura@quicinc.com>
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On 2/1/2024 12:24 AM, Maciej Żenczykowski wrote:

> 
> I believe so, yes.
> 
> I believe they are trying to avoid having to send ZLPs.
> That's determined *purely* by the size of things as they show up on
> the usb cable (ie. the size of the usb xfer).
> ie. that's where things that are a multiple of 512 (USB2) or 1024
> (USB3) need an extra 0 byte sized packet to prevent ZLP.
> 
> The actual size of the NTB doesn't matter.
> 
> That said... maybe we're overcomplicating this...
> Maybe it's enough to just remove this modulo check entirely (I know I
> asked for it before).
> 
> Ultimately if we just do:
> 
> // Windows NCM driver avoids USB ZLPs by adding a 1-byte zero pad as needed
> if (to_process == 1 && !*(u8*)(ntb_ptr + block_len)) --to_process;
> 
> it'll fix the problem too, and perhaps be easier to understand?
> 
I agree. This will simplify the check and also cover all cases.
To keep diff minimal from tested version (because issue comes up easily 
with a particular test here), I can remove the second check in the if 
block in the v2 and push it as v3.

Regards,
Krishna,