linux-kernel - Re: [PATCH] carl9170: remove redundant assignment to variable tx

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Message-ID: <c74e7d6b-8449-c551-fead-09f51688c5bd@gmail.com>
Date:   Mon, 24 Jan 2022 09:22:09 +0100
From:   Christian Lamparter <chunkeey@...il.com>
To:     Colin Ian King <colin.i.king@...il.com>,
        Christian Lamparter <chunkeey@...glemail.com>,
        Kalle Valo <kvalo@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] carl9170: remove redundant assignment to variable
 tx_params

On 23/01/2022 19:27, Colin Ian King wrote:
> Variable tx_params is being assigned a value that is never read, it
> is being re-assigned a couple of statements later with a different
> value. The assignment is redundant and can be removed.

I think you found a bug instead. This affects 1x2 AR9170 devices.
That IEEE80211_HT_MCS_TX_RX_DIFF capability flag should not be lost.

 From what I can tell, the next line (1917) after that WARN_ON(!(tx_streams >= ...)
that's still in the diff below:

                 tx_params = (tx_streams - 1) <<
                             IEEE80211_HT_MCS_TX_MAX_STREAMS_SHIFT;

needs a bitwise OR assignment operator instead of the direct assignment.

                 tx_params |= (tx_streams - 1) <<
                             IEEE80211_HT_MCS_TX_MAX_STREAMS_SHIFT;

can you please respin your patch and add stable?

Cheers,
Christian

> 
> Signed-off-by: Colin Ian King <colin.i.king@...il.com>
> ---
>   drivers/net/wireless/ath/carl9170/main.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/carl9170/main.c b/drivers/net/wireless/ath/carl9170/main.c
> index 49f7ee1c912b..f392a2ac7e14 100644
> --- a/drivers/net/wireless/ath/carl9170/main.c
> +++ b/drivers/net/wireless/ath/carl9170/main.c
> @@ -1909,8 +1909,6 @@ static int carl9170_parse_eeprom(struct ar9170 *ar)
>   	tx_streams = hweight8(ar->eeprom.tx_mask);
>   
>   	if (rx_streams != tx_streams) {
> -		tx_params = IEEE80211_HT_MCS_TX_RX_DIFF;
> -
>   		WARN_ON(!(tx_streams >= 1 && tx_streams <=
>   			IEEE80211_HT_MCS_TX_MAX_STREAMS));
>