netdev - Re: [PATCH net 0/4] Fix bit timings for m_can

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Date:   Thu, 18 Nov 2021 15:47:47 +0100
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Felipe Balbi (Intel)" <balbi@...nel.org>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH net 0/4] Fix bit timings for m_can_pci (Elkhart Lake)

On Wed, 2021-11-17 at 14:14 +0200, Jarkko Nikula wrote:
> Hi
> 
> On 11/16/21 3:58 PM, Matthias Schiffer wrote:
> > I just noticed that m_can_pci is completely broken on 5.15.2, while
> > it's working fine on 5.14.y.
> > 
> 
> Hmm.. so that may explain why I once saw candump received just zeroes on 
> v5.15-rc something but earlier kernels were ok. What's odd then next 
> time v5.15-rc was ok so went blaming sun spots instead of bisecting.
> 
> > I assume something simliar to [1] will be necessary in m_can_pci as
> > well, however I'm not really familiar with the driver. There is no
> > "mram_base" in m_can_plat_pci, only "base". Is using "base" with
> > iowrite32/ioread32 + manual increment the correct solution here?
> > 
> > 
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=99d173fbe8944861a00ebd1c73817a1260d21e60
> > 
> 
> If your test case after 5.15 reliably fails are you able to bisect or 
> check does the regression originate from the same commit?
> 
> Jarkko

The Fixes tag of 99d173fbe894 ("can: m_can: fix iomap_read_fifo() and
iomap_write_fifo()") is off AFAICT, the actual breakage happened with
812270e5445b ("can: m_can: Batch FIFO writes during CAN transmit") and
1aa6772f64b4 ("can: m_can: Batch FIFO reads during CAN receive");
reverting these two patches fixes the regression.

I just sent a patch for m_can_pci that applies the same fix that was
done in m_can_platform in 99d173fbe894, and verified that this makes
CAN communication work on Elkhart Lake with Linux 5.15.y together with
my other patches.

Matthias