netdev - Re: [PATCH net v2 1/1] net: ravb: Wait for operation mode to be applied

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Date: Mon, 1 Jan 2024 23:49:06 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: claudiu beznea <claudiu.beznea@...on.dev>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<yoshihiro.shimoda.uh@...esas.com>, <wsa+renesas@...g-engineering.com>,
	<mitsuhiro.kimura.kc@...esas.com>
CC: <netdev@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH net v2 1/1] net: ravb: Wait for operation mode to be
 applied

On 12/29/23 6:07 PM, claudiu beznea wrote:

[...]

>>>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>>>
>>>>> CSR.OPS bits specify the current operating mode and (according to
>>>>> documentation) they are updated by HW when the operating mode change
>>>>> request is processed. To comply with this check CSR.OPS before proceeding.
>>>>>
>>>>> Commit introduces ravb_set_opmode() that does all the necessities for
>>>>> setting the operating mode (set DMA.CCC and wait for CSR.OPS) and call it
>>>>> where needed. This should comply with all the HW manuals requirements as
>>>>> different manual variants specify that different modes need to be checked
>>>>> in CSR.OPS when setting DMA.CCC.
>>>>>
>>>>> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
>>>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>>> ---
>>>>>  drivers/net/ethernet/renesas/ravb_main.c | 52 ++++++++++++++----------
>>>>>  1 file changed, 31 insertions(+), 21 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>>>>> index 664eda4b5a11..ae99d035a3b6 100644
>>>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>>>>> @@ -66,14 +66,15 @@ int ravb_wait(struct net_device *ndev, enum ravb_reg reg, u32 mask, u32 value)
>>>>>  	return -ETIMEDOUT;
>>>>>  }
>>>>>  
>>>>> -static int ravb_config(struct net_device *ndev)
>>>>> +static int ravb_set_opmode(struct net_device *ndev, u32 opmode)
>>>>
>>>>    Since you pass the complete CCC register value below, you should
>>>> rather call the function ravb_set_ccc() and call the parameter opmode
>>>> ccc.
>>>
>>> This will be confusing. E.g., if renaming it ravb_set_ccc() one would
>>> expect to set any fields of CCC though this function but this is not true
>>> as ravb_modify() in this function masks only CCC_OPC. The call of:
>>>
>>> error = ravb_set_opmode(ndev, CCC_OPC_CONFIG | CCC_GAC | CCC_CSEL_HPB);
>>>
>>> bellow is just to comply with datasheet requirements, previous code and at
>>> the same time re-use this function.
>>
>>    How about the following then (ugly... but does the job):
>>
>> 	/* Set operating mode */
>> 	if (opmode & ~CCC_OPC)
>> 		ravb_write(ndev, opmode, CCC);
>> 	else
>> 		ravb_modify(ndev, CCC, CCC_OPC, opmode);
>>
>>    Either that or just don't use ravb_set_opmode() when writing the whole
>> 32-bit value below...
> 
> This looks uglier to me...
> 
> We have this discussion because of ccc_gac. For ccc_gac platforms we need
> to set OPC, GAC, CSEL at the same time. This is how we can change the
> operating mode to configuration mode in case we also need to configure GAC
> (due to restrictions imposed by hardware).
> 
> What I want to say is that setting GAC and CSEL along with CCC is part of
> changing the operating mode to configuration mode for platforms supporting
> GAC because of hardware limitations.

   After thinking about it once more, your description seems correct.
But then we need something like this:

static int ravb_set_opmode(struct net_device *ndev, u32 opmode)
{
	u32 ccc_mask = CCC_OPC;
	u32 csr_ops = 1U << (opmode & CCC_OPC);
 	int error;

 	if (opmode & CCC_GAC)
 		ccc_mask |= CCC_CSEL;

	/* Set operating mode */
	ravb_modify(ndev, CCC, ccc_mask, opmode);
	/* Check if the operating mode is changed to the requested one */
	error = ravb_wait(ndev, CSR, CSR_OPS, csr_ops);
 	if (error)
 		netdev_err(ndev, "failed to switch device to  requested mode\n");

	return error;
}

[...]

MBR, Sergey