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

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Date:   Tue, 16 Nov 2021 14:58:19 +0100
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Felipe Balbi (Intel)" <balbi@...nel.org>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 0/4] Fix bit timings for m_can_pci (Elkhart Lake)

On Mon, 2021-11-15 at 10:18 +0100, Matthias Schiffer wrote:
> This series fixes two issues we found with the setup of the CAN
> controller of Intel Elkhart Lake CPUs:
> 
> - Patch 1 fixes an incorrect reference clock rate, which caused the
>   configured and the actual bitrate always to differ by a factor of 2.
> - Patches 2-4 fix a deviation between the driver and the documentation.
>   We did not actually see issues without these patches, however we did
>   only superficial testing and may just not have hit the specific
>   bittiming values that violate the documented limits.
> 
> 
> Matthias Schiffer (4):
>   can: m_can: pci: fix incorrect reference clock rate
>   Revert "can: m_can: remove support for custom bit timing"
>   can: m_can: make custom bittiming fields const
>   can: m_can: pci: use custom bit timings for Elkhart Lake
> 
>  drivers/net/can/m_can/m_can.c     | 24 ++++++++++++----
>  drivers/net/can/m_can/m_can.h     |  3 ++
>  drivers/net/can/m_can/m_can_pci.c | 48 ++++++++++++++++++++++++++++---
>  3 files changed, 65 insertions(+), 10 deletions(-)
> 

I just noticed that m_can_pci is completely broken on 5.15.2, while
it's working fine on 5.14.y.

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