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Date:   Mon, 29 Apr 2019 10:26:52 +0200
From:   Alexandre Torgue <alexandre.torgue@...com>
To:     biao huang <biao.huang@...iatek.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 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.
> 
> 
> 

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