mac80211 TX frame alignment

mac80211 TX frame alignment

[Ivo van Doorn]

Hi Johannes,

Do you know if for outgoing frames the header should always
be 4-byte aligned?
I have a bugreport from users claiming that master mode
is failing for rt2500pci because the beacons passed to the
driver are not 4-byte aligned which causes the device not
to send out the beacons correctly.

I'm just wondering if this is something that should be fixed
in the driver or in mac80211.

Thanks,

Ivo

Re: mac80211 TX frame alignment

[Johannes Berg]

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Hi Ivo,

> Do you know if for outgoing frames the header should always
> be 4-byte aligned?

I know that there's no alignment guarantee.

> I have a bugreport from users claiming that master mode
> is failing for rt2500pci because the beacons passed to the
> driver are not 4-byte aligned which causes the device not
> to send out the beacons correctly.
> 
> I'm just wondering if this is something that should be fixed
> in the driver or in mac80211.

I don't think we can fix that in mac80211, since we don't know whether
or not any alignment is required. We could align beacon frames, I
suppose, since those are created on the fly, but not data frames.

johannes

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Re: mac80211 TX frame alignment

[Ivo van Doorn]

Hi,

> > Do you know if for outgoing frames the header should always
> > be 4-byte aligned?
> 
> I know that there's no alignment guarantee.
>
> > I have a bugreport from users claiming that master mode
> > is failing for rt2500pci because the beacons passed to the
> > driver are not 4-byte aligned which causes the device not
> > to send out the beacons correctly.
> > 
> > I'm just wondering if this is something that should be fixed
> > in the driver or in mac80211.
> 
> I don't think we can fix that in mac80211, since we don't know whether
> or not any alignment is required. We could align beacon frames, I
> suppose, since those are created on the fly, but not data frames.

Ok, I'll look into a patch for making sure rt2x00 aligns all frames
correctly before mapping the DMA.

Thanks,

Ivo