linux-kernel - Re: [PATCH net 1/2] net: ravb: Wait for operation mode to be applied

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Date: Wed, 20 Dec 2023 13:27:43 +0200
From: claudiu beznea <claudiu.beznea@...on.dev>
To: Sergey Shtylyov <s.shtylyov@....ru>, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 claudiu.beznea.uj@...renesas.com, yoshihiro.shimoda.uh@...esas.com,
 wsa+renesas@...g-engineering.com, niklas.soderlund+renesas@...natech.se,
 biju.das.jz@...renesas.com, prabhakar.mahadev-lad.rj@...renesas.com,
 mitsuhiro.kimura.kc@...esas.com, geert+renesas@...der.be
Cc: netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: ravb: Wait for operation mode to be applied



On 19.12.2023 18:49, Sergey Shtylyov wrote:
> On 12/15/23 1:04 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 when the operating mode change request
>>>> is processed. Thus, check CSR.OPS before proceeding.
>>>
>>>    The manuals I have indeed say we need to check CSR.OPS... But we only
>>> need to wait iff we transfer from the operation mode to the config mode...
>>
>> RZ/G3S manual say about CSR.OPS "These bits are updated when an operating
> 
>    I was unable to find the RZ/G3 manuals on ther Renesas' website... :-(
> 
>> mode changes is processed". From this I get we need to check it for any mode.
> 
>   I don't argue with the (safety) checking of CSR.OPS, I was just pointing
> out that the R-Car gen3 manual says that only transfer from operation to
> the config mode happens after a considerable amount of time, other transfers
> do happen immediately after updating CCC.OPC.
> 
>> Also, on configuration procedure (of RZ/G3S) it say CSR.OPS need to be
>> checked when switching from reset -> config.
> 
>    Just checked or waited on?

Manual say to check that the read value of CSR.OPS=2

>    The R-car does have a specific algorithm for transferring from the operation
> to the reset mode (you need to set CC.DTSR first and then wait for CSR.DTS to
> clear before updating CCC.OPC)...

In the stop procedure chapter of RZ/G3S manual, as the setup of DMAC.CCC=0
is the last operation that needs to be done, it doesn't specify either that
CSR needs to be checked.

> 
> [...]
> 
>>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>> ---
>>>>  drivers/net/ethernet/renesas/ravb_main.c | 47 ++++++++++++++++++++----
>>>>  1 file changed, 39 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>>>> index 9178f6d60e74..ce95eb5af354 100644
>>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> [...]
>>>> @@ -1744,6 +1747,18 @@ static inline int ravb_hook_irq(unsigned int irq, irq_handler_t handler,
>>>>  	return error;
>>>>  }
>>>>  
>>>> +static int ravb_set_reset_mode(struct net_device *ndev)
>>>> +{
>>>> +	int error;
>>>> +
>>>> +	ravb_write(ndev, CCC_OPC_RESET, CCC);
>>>> +	error = ravb_wait(ndev, CSR, CSR_OPS, CSR_OPS_RESET);
>>>> +	if (error)
>>>> +		netdev_err(ndev, "failed to switch device to reset mode\n");
>>>> +
>>>> +	return error;
>>>> +}
>>>> +
>>>
>>>    Again, ravb_wait() call doesn't seem necessary here...
>>
>> Ok. I followed the guideline from the description of CSR.OPS. Let me know
>> if you want to keep it or not. I think I haven't saw any issues w/o this.
> 
>   Yes, please remove the waiting.
> 
> [...]
> 
> MBR, Sergey