linux-kernel - Re: [PATCH 2/6] net: stmmac: fix csr

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Message-ID: <1556525353.24897.30.camel@mhfsdcap03>
Date:   Mon, 29 Apr 2019 16:09:13 +0800
From:   biao huang <biao.huang@...iatek.com>
To:     Alexandre Torgue <alexandre.torgue@...com>
CC:     Jose Abreu <joabreu@...opsys.com>, <davem@...emloft.net>,
        "Giuseppe Cavallaro" <peppe.cavallaro@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <netdev@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <yt.shen@...iatek.com>,
        <jianguo.zhang@...iatek.com>
Subject: Re: [PATCH 2/6] net: stmmac: fix csr_clk can't be zero issue

Hi,

On Mon, 2019-04-29 at 09:18 +0200, Alexandre Torgue wrote:
> Hi
> 
> On 4/28/19 8:30 AM, Biao Huang wrote:
> > The specific clk_csr value can be zero, and
> > stmmac_clk is necessary for MDC clock which can be set dynamically.
> > So, change the condition from plat->clk_csr to plat->stmmac_clk to
> > fix clk_csr can't be zero issue.
> > 
> > Signed-off-by: Biao Huang <biao.huang@...iatek.com>
> > ---
> >   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index 818ad88..9e89b94 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -4376,7 +4376,7 @@ int stmmac_dvr_probe(struct device *device,
> >   	 * set the MDC clock dynamically according to the csr actual
> >   	 * clock input.
> >   	 */
> > -	if (!priv->plat->clk_csr)
> > +	if (priv->plat->stmmac_clk)
> >   		stmmac_clk_csr_set(priv);
> >   	else
> >   		priv->clk_csr = priv->plat->clk_csr;
> > 
> 
> So, as soon as stmmac_clk will be declared, it is no longer possible to 
> fix a CSR through the device tree ?

let's focus on the condition:
1. clk_csr may be zero, it should not be the condition. or the clk_csr =
0 will jump to the wrong block.
2. Since stmmac_clk_csr_set will get_clk_rate from stmmac_clk,
the plat->stmmac_clk is a more proper condition.

In some case, it's impossible to get the clk rate of stmmac_clk,
so it's better to remain the clk_csr flow.