netdev - Re: [PATCH net-next 3/6] net: ipa: move and redefine ipa_version

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Message-ID: <be11181df759bce03b0bc049d30fd925d5229718.camel@redhat.com>
Date:   Tue, 20 Sep 2022 15:37:59 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Alex Elder <elder@...aro.org>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org
Cc:     mka@...omium.org, evgreen@...omium.org, andersson@...nel.org,
        quic_cpratapa@...cinc.com, quic_avuyyuru@...cinc.com,
        quic_jponduru@...cinc.com, quic_subashab@...cinc.com,
        elder@...nel.org, netdev@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 3/6] net: ipa: move and redefine
 ipa_version_valid()

On Tue, 2022-09-20 at 07:50 -0500, Alex Elder wrote:
> On 9/20/22 3:29 AM, Paolo Abeni wrote:
> > On Fri, 2022-09-09 at 20:11 -0500, Alex Elder wrote:
> > > Move the definition of ipa_version_valid(), making it a static
> > > inline function defined together with the enumerated type in
> > > "ipa_version.h".  Define a new count value in the type.
> > > 
> > > Rename the function to be ipa_version_supported(), and have it
> > > return true only if the IPA version supplied is explicitly supported
> > > by the driver.
> > 
> > I'm wondering if the above is going to cause regressions with some IPA
> > versions suddenly not probed anymore by the module?
> 
> That is a really good observation.
> 
> The way versions are handled is a little bit inconsistent.  The
> code is generally written in such a way that *any* version could
> be used (between a certain minimum and maximum, currently 3.0-4.11).
> In other words, the *intent* in the code is to make it so that
> quirks and features that are version-specific are handled the right
> way, even if we do not (yet) support it.
> 
> So for example the inline macro rsrc_grp_encoded() returns the
> mask to use to specify an endpoint's assigned resource group.
> IPA v4.7 uses one bit, whereas others use two or three bits.
> We don't "formally" support IPA v4.7, because I (or someone
> else) haven't set up a Device Tree file and "IPA config data"
> to test it on real hardware.  Still, rsrc_grp_encoded() returns
> the right value for IPA v4.7, even though it won't be needed
> until IPA v4.7 is tested and declared supported.
> 
> The intent is to facilitate adding support for IPA v4.7 (and
> others).  In principle one could simply try it out and it should
> work, but in reality it is unlikely to be that easy.
> 
> Finally, as mentioned, to support a version (such as 4.7) we
> need to create "ipa_data-v4.7.c", which defines a bunch of
> things that are version-specific.  Because those definitions
> are missing, no IPA v4.7 hardware will be matched by the
> ipa_match[] table.
> 
> So the answer to your question is that currently none of the
> unsupported versions will successfully probe anyway.
> 
> > Additionally there are a few places checking for the now unsupported
> > version[s], I guess that check could/should be removed? e.g.
> > ipa_reg_irq_suspend_en_ee_n_offset(),
> > ipa_reg_irq_suspend_info_ee_n_offset()
> > ...
> 
> I'm a fan of removing unused code like this, but I really would
> like to actually support these other IPA versions, and I hope
> the code is close to ready for that.  I would just need to get
> some hardware to test it with (and it needs to rise to the top
> of my priority list...).
> 
> Does this make sense to you?

Yes, very clear and detailed explaination, thanks!

I'm ok with the series in the current form.

Cheers,

Paolo