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

From: "Pali Rohár" <pali@kernel.org>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: "Jonas Dreßler" <verdre@v0yd.nl>,
	"Brian Norris" <briannorris@chromium.org>,
	"Amitkumar Karwar" <amitkarwar@gmail.com>,
	"Ganapathi Bhat" <ganapathi017@gmail.com>,
	"Xinming Hu" <huxinming820@gmail.com>,
	"Kalle Valo" <kvalo@codeaurora.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Tsuchiya Yuto" <kitakar@gmail.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	netdev@vger.kernel.org,
	"Linux Kernel" <linux-kernel@vger.kernel.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	"Maximilian Luz" <luzmaximilian@gmail.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>
Subject: Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes
Date: Thu, 23 Sep 2021 22:22:31 +0200	[thread overview]
Message-ID: <20210923202231.t2zjoejpxrbbe5hc@pali> (raw)
In-Reply-To: <CAHp75Vd5iCLELx8s+Zvcj8ufd2bN6CK26soDMkZyC1CwMO2Qeg@mail.gmail.com>

On Thursday 23 September 2021 22:41:30 Andy Shevchenko wrote:
> On Thu, Sep 23, 2021 at 6:28 PM Jonas Dreßler <verdre@v0yd.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.

This reminds me a discussion with Bjorn about CRS response returned
after firmware crash / reset when device is not ready yet:
https://lore.kernel.org/linux-pci/20210922164803.GA203171@bhelgaas/

Could not be this similar issue? You could check it via reading
PCI_VENDOR_ID register from config space. And if it is not valid value
then card is not really ready yet.

> 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