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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Cc:     linux-wireless@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] iwlwifi: mvm: don't send the IWL_MVM_RXQ_NSSN_SYNC notif to Rx queues
References: <20191120132628.30731-1-emmanuel.grumbach@intel.com>
        <20191121184530.5393-1-emmanuel.grumbach@intel.com>
Date:   Mon, 2 Dec 2019 14:43:53 +0000
In-Reply-To: <20191121184530.5393-1-emmanuel.grumbach@intel.com> (Emmanuel
        Grumbach's message of "Thu, 21 Nov 2019 20:45:30 +0200")
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Emmanuel Grumbach <emmanuel.grumbach@intel.com> writes:

> The purpose of this was to keep all the queues updated with
> the Rx sequence numbers because unlikely yet possible
> situations where queues can't understand if a specific
> packet needs to be dropped or not.
>
> Unfortunately, it was reported that this caused issues in
> our DMA engine. We don't fully understand how this is related,
> but this is being currently debugged. For now, just don't send
> this notification to the Rx queues. This de-facto reverts my
> commit 3c514bf831ac12356b695ff054bef641b9e99593:
>
> iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues
>
> This issue was reported here:
> https://bugzilla.kernel.org/show_bug.cgi?id=204873
> https://bugzilla.kernel.org/show_bug.cgi?id=205001
> and others maybe.
>
> Fixes: 3c514bf831ac ("iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues")
> CC: <stable@vger.kernel.org> # 5.3+
> Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
> ---
> v2: avoid the unused variable warning
> ---
>  drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c | 22 ++++++++++++-------
>  1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c b/drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c
> index 75a7af5ad7b2..392bfa4b496c 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c
> @@ -514,14 +514,20 @@ static bool iwl_mvm_is_sn_less(u16 sn1, u16 sn2, u16 buffer_size)
>  
>  static void iwl_mvm_sync_nssn(struct iwl_mvm *mvm, u8 baid, u16 nssn)
>  {
> -	struct iwl_mvm_rss_sync_notif notif = {
> -		.metadata.type = IWL_MVM_RXQ_NSSN_SYNC,
> -		.metadata.sync = 0,
> -		.nssn_sync.baid = baid,
> -		.nssn_sync.nssn = nssn,
> -	};
> -
> -	iwl_mvm_sync_rx_queues_internal(mvm, (void *)&notif, sizeof(notif));
> +	/*
> +	 * This allow to synchronize the queues, but it has been reported
> +	 * to cause FH issues. Don't send the notification for now.
> +	 *
> +	 * struct iwl_mvm_rss_sync_notif notif = {
> +	 *	.metadata.type = IWL_MVM_RXQ_NSSN_SYNC,
> +	 *	.metadata.sync = 0,
> +	 *	.nssn_sync.baid = baid,
> +	 *	.nssn_sync.nssn = nssn,
> +	 * };
> +	 *
> +	 *
> +	 * iwl_mvm_sync_rx_queues_internal(mvm, (void *)&notif, sizeof(notif));
> +	 */

Please don't comment out code, instead remove entirely. You can find the
old code from the git history anyway.

-- 
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches