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From:   Kalle Valo <kvalo@kernel.org>
To:     Luca Coelho <luca@coelho.fi>
Cc:     linux-wireless@vger.kernel.org
Subject: Re: [PATCH for v5.17 6/8] iwlwifi: mei: retry mapping the shared area
References: <20220128123057.524038-1-luca@coelho.fi>
        <iwlwifi.20220128142706.cc51e6a6d635.I4b74a082eb8d89f9e4f556a27c4339c15444dc6c@changeid>
Date:   Thu, 03 Feb 2022 10:16:03 +0200
In-Reply-To: <iwlwifi.20220128142706.cc51e6a6d635.I4b74a082eb8d89f9e4f556a27c4339c15444dc6c@changeid>
        (Luca Coelho's message of "Fri, 28 Jan 2022 14:30:55 +0200")
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Luca Coelho <luca@coelho.fi> writes:

> From: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
>
> The shared area is a DMA memory allocated in the host and
> mapped so that the host and the CSME firmware can
> exchange data. It is mapped through a dedicated PCI device
> that is driven by the mei bus driver.
>
> The bus driver is in charge of allocating and mapping this
> memory. It also needs to configure the CSME firmware with
> a specific set of commands, so that the CSME firmware will
> know that this memory is meant to be used by its internal
> WLAN module.
>
> For this, the CSME firmware first needs to completely
> initialize its WLAN module and only then get the mapping
> request.
>
> The problem is that the mei bus enumeration completes
> before the WLAN is completely ready. This means that
> the WLAN module's initialization is racing with iwlmei's
> allocation and mapping flow.
>
> Testing showed a problem in resume flows where iwlmei
> was too fast and the DMA mapping failed.
>
> Add a retry mechanism to make sure that we will succeed
> to map the memory.
>
> Fixes: 2da4366f9e2c ("iwlwifi: mei: add the driver to allow cooperation with CSME")
> Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
> Fixes: bcbddc4f9d02 ("iwlwifi: mei: wait before mapping the shared area")

I'll move the latter Fixes before s-o-b tag.

> -	/*
> -	 * The CSME firmware needs to boot the internal WLAN client. Wait here
> -	 * so that the DMA map request will succeed.
> -	 */
> -	msleep(20);
> +	do {
> +		ret = iwl_mei_alloc_shared_mem(cldev);
> +		if (!ret)
> +			break;
> +		/*
> +		 * The CSME firmware needs to boot the internal WLAN client.
> +		 * This can take time in certain configurations (usually
> +		 * upon resume and when the whole CSME firmware is shut down
> +		 * during suspend).
> +		 *
> +		 * Wait a bit before retrying and hope we'll succeed next time.
> +		 */
>  
> -	ret = iwl_mei_alloc_shared_mem(cldev);
> -	if (ret)
> +		dev_dbg(&cldev->dev,
> +			"Couldn't allocate the shared memory: %d, attempt %d / %d\n",
> +			ret, alloc_retry, ALLOC_SHARED_MEM_RETRY_MAX_NUM);
> +		msleep(100);
> +		alloc_retry--;
> +	} while (alloc_retry);

Nitpicking, but this could have been:

while (alloc_retry--);

But no need to resend because of this.

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