netdev - Re: [PATCH v2 2/2] ath9k: of

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Date:   Mon, 17 Apr 2023 19:54:24 +0200
From:   Álvaro Fernández Rojas <noltari@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     f.fainelli@...il.com, jonas.gorski@...il.com, nbd@....name,
        kvalo@...nel.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, chunkeey@...il.com,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] ath9k: of_init: add endian check

El lun, 17 abr 2023 a las 11:21, Toke Høiland-Jørgensen
(<toke@...e.dk>) escribió:
>
> Álvaro Fernández Rojas <noltari@...il.com> writes:
>
> > BCM63xx (Big Endian MIPS) devices store the calibration data in MTD
> > partitions but it needs to be swapped in order to work, otherwise it fails:
> > ath9k 0000:00:01.0: enabling device (0000 -> 0002)
> > ath: phy0: Ignoring endianness difference in EEPROM magic bytes.
> > ath: phy0: Bad EEPROM VER 0x0001 or REV 0x00e0
> > ath: phy0: Unable to initialize hardware; initialization status: -22
> > ath9k 0000:00:01.0: Failed to initialize device
> > ath9k: probe of 0000:00:01.0 failed with error -22
> >
> > For compatibility with current devices the AH_NO_EEP_SWAP flag will be
> > activated only when qca,endian-check isn't present in the device tree.
> > This is because some devices have the magic values swapped but not the actual
> > EEPROM data, so activating the flag for those devices will break them.
> >
> > Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> > ---
> >  drivers/net/wireless/ath/ath9k/init.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/wireless/ath/ath9k/init.c b/drivers/net/wireless/ath/ath9k/init.c
> > index 4f00400c7ffb..abde953aec61 100644
> > --- a/drivers/net/wireless/ath/ath9k/init.c
> > +++ b/drivers/net/wireless/ath/ath9k/init.c
> > @@ -615,7 +615,6 @@ static int ath9k_nvmem_request_eeprom(struct ath_softc *sc)
> >
> >       ah->nvmem_blob_len = len;
> >       ah->ah_flags &= ~AH_USE_EEPROM;
> > -     ah->ah_flags |= AH_NO_EEP_SWAP;
> >
> >       return 0;
> >  }
> > @@ -688,9 +687,11 @@ static int ath9k_of_init(struct ath_softc *sc)
> >                       return ret;
> >
> >               ah->ah_flags &= ~AH_USE_EEPROM;
> > -             ah->ah_flags |= AH_NO_EEP_SWAP;
> >       }
> >
> > +     if (!of_property_read_bool(np, "qca,endian-check"))
> > +             ah->ah_flags |= AH_NO_EEP_SWAP;
> > +
>
> So I'm not sure just setting (or not) this flag actually leads to
> consistent behaviour. The code in ath9k_hw_nvram_swap_data() that reacts
> to this flag does an endianness check before swapping, and the behaviour
> of this check depends on the CPU endianness. However, the byte swapping
> you're after here also swaps u8 members of the eeprom, so it's not
> really a data endianness swap, and I don't think it should depend on the
> endianness of the CPU?
>
> So at least conceptually, the magic byte check in
> ath9k_hw_nvram_swap_data() is wrong; instead the byteswap check should
> just be checking against the little-endian version of the firmware
> (i.e., 0xa55a; I think that's what your device has, right?). However,
> since we're setting an explicit per-device property anyway (in the
> device tree), maybe it's better to just have that be an "eeprom needs
> swapping" flag and do the swap unconditionally if it's set? I think that
> would address Krzysztof's comment as well ("needs swapping" is a
> hardware property, "do the check" is not).

Yes, you're right, it's probably better to introduce a new and more
clear flag that swaps the content inconditionally.

>
> Now, the question becomes whether the "check" code path is actually used
> for anything today? The old mail thread I quoted in the other thread
> seems to indicate it's not, but it's not quite clear from the code
> whether there's currently any way to call into
> ath9k_hw_nvram_swap_data() without the NO_EEP_SWAP flag being set?

It's only used when endian_check is enabled in ath9k_platform_data:
https://github.com/torvalds/linux/blob/6a8f57ae2eb07ab39a6f0ccad60c760743051026/drivers/net/wireless/ath/ath9k/init.c#L645
We're currently using it on OpenWrt for bmips:
https://github.com/Noltari/openwrt/blob/457549665fcb93667453ef48c50bf43eddd776ef/target/linux/bmips/files/arch/mips/bmips/ath9k-fixup.c#L198-L199

>
> WDYT?
>
> -Toke