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

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Date:   Tue, 30 Apr 2019 11:43:52 +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 4/30/19 11:15 AM, biao huang wrote:
> 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);
>

Yes, I agree.
Thanks
Alex


>>>
>>>
> 
>