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

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Date:   Tue, 30 Apr 2019 17:15:45 +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

On Mon, 2019-04-29 at 10:26 +0200, Alexandre Torgue wrote:
> 
> On 4/29/19 10:09 AM, biao huang wrote:
> > 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.
> > 
> 
> Ok, but here you remove one possibility: stmmac_clk and clk_csr defined. 
> no ?
> 
> Other way could be the following code + initialize priv->plat->clk_csr 
> with a non null value before read it in device tree (in stmmac_platform).
> 
> if (priv->plat->clk_csr >= 0)
> 	priv->clk_csr = priv->plat->clk_csr;
> else
> 	stmmac_clk_csr_set(priv);
> 
> 
> 
> > In some case, it's impossible to get the clk rate of stmmac_clk,
> > so it's better to remain the clk_csr flow.
> > 
Agree.

Maybe we should initialize plat->clk_csr to -1
in stmmac_probe_config_dt:

plat->clk_csr = -1;
/* Get clk_csr from device tree */                                      
of_property_read_u32(np, "clk_csr", &plat->clk_csr); 

Then the condition can write as you proposed:
if (priv->plat->clk_csr >= 0)
 	priv->clk_csr = priv->plat->clk_csr;
else
 	stmmac_clk_csr_set(priv);

> > 
> >