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

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Date:   Thu, 23 Sep 2021 22:41:30 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jonas Dreßler <verdre@...d.nl>
Cc:     Brian Norris <briannorris@...omium.org>,
        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>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        netdev@...r.kernel.org,
        Linux Kernel <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 Thu, Sep 23, 2021 at 6:28 PM Jonas Dreßler <verdre@...d.nl> wrote:
> On 9/22/21 2:50 PM, Jonas Dreßler wrote:

...

> - Just calling mwifiex_write_reg() once and then blocking until the card
> wakes up using my delay-loop doesn't fix the issue, it's actually
> writing multiple times that fixes the issue
>
> These observations sound a lot like writes (and even reads) are actually
> being dropped, don't they?

It sounds like you're writing into a not ready (fully powered on) device.

To check this, try to put a busy loop for reading and check the value
till it gets 0.

Something like

  unsigned int count = 1000;

  do {
    if (mwifiex_read_reg(...) == 0)
      break;
  } while (--count);


-- 
With Best Regards,
Andy Shevchenko