linux-kernel - Re: [PATCH net v3] net: macb: Correct usage of MACB_CAPS_CLK_HW

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Message-ID: <8f36997b-2310-0579-173d-17f532a54d8d@microchip.com>
Date:   Mon, 4 Jan 2021 14:04:06 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <ckeepax@...nsource.cirrus.com>, <Nicolas.Ferre@...rochip.com>,
        <davem@...emloft.net>, <kuba@...nel.org>
CC:     <andrew@...n.ch>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v3] net: macb: Correct usage of MACB_CAPS_CLK_HW_CHG
 flag

Hi Charles,

On 04.01.2021 12:38, Charles Keepax wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> A new flag MACB_CAPS_CLK_HW_CHG was added and all callers of
> macb_set_tx_clk were gated on the presence of this flag.
> 
> -   if (!clk)
> + if (!bp->tx_clk || !(bp->caps & MACB_CAPS_CLK_HW_CHG))
> 
> However the flag was not added to anything other than the new
> sama7g5_gem, turning that function call into a no op for all other
> systems. This breaks the networking on Zynq.
> 
> The commit message adding this states: a new capability so that
> macb_set_tx_clock() to not be called for IPs having this
> capability
> 
> This strongly implies that present of the flag was intended to skip
> the function not absence of the flag. Update the if statement to
> this effect, which repairs the existing users.

Yes, the presence of the flag should involve skipping the calling of
clk_set_rate() since the IP logic would take care of proper clock division
depending on the link speed. I wrongly cherry pick this one from internal
branches. Sorry for this breakage.

> 
> Fixes: daafa1d33cc9 ("net: macb: add capability to not set the clock rate")
> Suggested-by: Andrew Lunn <andrew@...n.ch>
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Reviewed-by: Claudiu Beznea <claudiu.beznea@...rochip.com>

> ---
> 
> Changes since v1:
>  - Updated flag semantics to skip function, as appears to have been
>    intended by the initial commit.
> 
> Changes since v2:
>  - Adding "net" to the subject line
> 
> Thanks,
> Charles
> 
>  drivers/net/ethernet/cadence/macb_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index d5d910916c2e8..814a5b10141d1 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -467,7 +467,7 @@ static void macb_set_tx_clk(struct macb *bp, int speed)
>  {
>         long ferr, rate, rate_rounded;
> 
> -       if (!bp->tx_clk || !(bp->caps & MACB_CAPS_CLK_HW_CHG))
> +       if (!bp->tx_clk || (bp->caps & MACB_CAPS_CLK_HW_CHG))
>                 return;
> 
>         switch (speed) {
> --
> 2.11.0
>