netdev - Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes

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Date:   Mon, 30 Aug 2021 15:49:09 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jonas Dreßler <verdre@...d.nl>
Cc:     Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Tsuchiya Yuto <kitakar@...il.com>,
        "open list:TI WILINK WIRELES..." <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Pali Rohár <pali@...nel.org>
Subject: Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes

On Mon, Aug 30, 2021 at 3:38 PM Jonas Dreßler <verdre@...d.nl> wrote:
>
> On the 88W8897 card it's very important the TX ring write pointer is
> updated correctly to its new value before setting the TX ready
> interrupt, otherwise the firmware appears to crash (probably because
> it's trying to DMA-read from the wrong place).
>
> Since PCI uses "posted writes" when writing to a register, it's not
> guaranteed that a write will happen immediately. That means the pointer
> might be outdated when setting the TX ready interrupt, leading to
> firmware crashes especially when ASPM L1 and L1 substates are enabled
> (because of the higher link latency, the write will probably take
> longer).
>
> So fix those firmware crashes by always forcing non-posted writes. We do
> that by simply reading back the register after writing it, just as a lot
> of other drivers do.
>
> There are two reproducers that are fixed with this patch:
>
> 1) During rx/tx traffic and with ASPM L1 substates enabled (the enabled
> substates are platform dependent), the firmware crashes and eventually a
> command timeout appears in the logs. That crash is fixed by using a
> non-posted write in mwifiex_pcie_send_data().
>
> 2) When sending lots of commands to the card, waking it up from sleep in
> very quick intervals, the firmware eventually crashes. That crash
> appears to be fixed by some other non-posted write included here.

Thanks for all this work!

Nevertheless, do we have any commits that may be a good candidate to
be in the Fixes tag here?

> Signed-off-by: Jonas Dreßler <verdre@...d.nl>
> ---
>  drivers/net/wireless/marvell/mwifiex/pcie.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/pcie.c b/drivers/net/wireless/marvell/mwifiex/pcie.c
> index c6ccce426b49..bfd6e135ed99 100644
> --- a/drivers/net/wireless/marvell/mwifiex/pcie.c
> +++ b/drivers/net/wireless/marvell/mwifiex/pcie.c
> @@ -237,6 +237,12 @@ static int mwifiex_write_reg(struct mwifiex_adapter *adapter, int reg, u32 data)
>
>         iowrite32(data, card->pci_mmap1 + reg);
>
> +       /* Do a read-back, which makes the write non-posted, ensuring the
> +        * completion before returning.

> +        * The firmware of the 88W8897 card is buggy and this avoids crashes.

Any firmware version reference? Would be nice to have just for the
sake of record.

> +        */
> +       ioread32(card->pci_mmap1 + reg);
> +
>         return 0;
>  }


-- 
With Best Regards,
Andy Shevchenko