netdev - Re: [PATCH] ath9k: Check for errors when reading SREV register

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Message-ID: <87va0cpmt4.fsf@codeaurora.org>
Date:   Thu, 21 Mar 2019 12:02:47 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Tim Schumacher <timschumi@....de>
Cc:     QCA ath9k Development <ath9k-devel@....qualcomm.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ath9k: Check for errors when reading SREV register

Tim Schumacher <timschumi@....de> writes:

> Right now, if an error is encountered during the SREV register
> read (i.e. an EIO in ath9k_regread()), that error code gets
> passed all the way to __ath9k_hw_init(), where it is visible
> during the "Chip rev not supported" message.
>
>     ath9k_htc 1-1.4:1.0: ath9k_htc: HTC initialized with 33 credits
>     ath: phy2: Mac Chip Rev 0x0f.3 is not supported by this driver
>     ath: phy2: Unable to initialize hardware; initialization status: -95
>     ath: phy2: Unable to initialize hardware; initialization status: -95
>     ath9k_htc: Failed to initialize the device
>
> Check for -EIO explicitly in ath9k_hw_read_revisions() and return
> a boolean based on the success of the operation. Check for that in
> __ath9k_hw_init() and abort with a more debugging-friendly message
> if reading the revisions wasn't successful.
>
>     ath9k_htc 1-1.4:1.0: ath9k_htc: HTC initialized with 33 credits
>     ath: phy2: Failed to read SREV register
>     ath: phy2: Could not read hardware revision
>     ath: phy2: Unable to initialize hardware; initialization status: -95
>     ath: phy2: Unable to initialize hardware; initialization status: -95
>     ath9k_htc: Failed to initialize the device
>
> This helps when debugging by directly showing the first point of
> failure and it could prevent possible errors if a 0x0f.3 revision
> is ever supported.
>
> Signed-off-by: Tim Schumacher <timschumi@....de>

[...]

> -	val = REG_READ(ah, AR_SREV) & AR_SREV_ID;
> +	srev = REG_READ(ah, AR_SREV);
> +
> +	if (srev == -EIO) {
> +		ath_err(ath9k_hw_common(ah),
> +			"Failed to read SREV register");
> +		return false;
> +	}

I really don't like how the error handling is implemented in REG_READ().
If the register has value 0xfffffffb (= -EIO ==-5) won't this interpret
that as an error?

-- 
Kalle Valo