netdev - Re: [PATCH net-next v2 1/8] ravb: Add struct ravb_hw

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Date:   Tue, 17 Aug 2021 23:11:06 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Biju Das <biju.das.jz@...renesas.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sergey Shtylyov <s.shtylyov@...russia.ru>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Adam Ford <aford173@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Yuusuke Ashizuka <ashiduka@...itsu.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH net-next v2 1/8] ravb: Add struct ravb_hw_info to driver
 data

On 8/17/21 2:24 PM, Biju Das wrote:

[...]
>>>>> -----Original Message-----
>>>>> On Mon, Aug 2, 2021 at 12:27 PM Biju Das
>>>>> <biju.das.jz@...renesas.com>
>>>>> wrote:
>>>>>> The DMAC and EMAC blocks of Gigabit Ethernet IP found on RZ/G2L
>>>>>> SoC are similar to the R-Car Ethernet AVB IP. With a few changes
>>>>>> in the driver we can support both IPs.
>>>>>>
>>>>>> Currently a runtime decision based on the chip type is used to
>>>>>> distinguish the HW differences between the SoC families.
>>>>>>
>>>>>> The number of TX descriptors for R-Car Gen3 is 1 whereas on
>>>>>> R-Car
>>>>>> Gen2 and RZ/G2L it is 2. For cases like this it is better to
>>>>>> select the number of TX descriptors by using a structure with a
>>>>>> value, rather than a runtime decision based on the chip type.
>>>>>>
>>>>>> This patch adds the num_tx_desc variable to struct ravb_hw_info
>>>>>> and also replaces the driver data chip type with struct
>>>>>> ravb_hw_info by moving chip type to it.
>>>>>>
>>>>>> Signed-off-by: Biju Das <biju.das.jz@...renesas.com>
>>>>>> Reviewed-by: Lad Prabhakar
>>>>>> <prabhakar.mahadev-lad.rj@...renesas.com>
>>>>>
>>>>> Thanks for your patch!
>>>>>
>>>>>> --- a/drivers/net/ethernet/renesas/ravb.h
>>>>>> +++ b/drivers/net/ethernet/renesas/ravb.h
>>>>>> @@ -988,6 +988,11 @@ enum ravb_chip_id {
>>>>>>         RCAR_GEN3,
>>>>>>  };
>>>>>>
>>>>>> +struct ravb_hw_info {
>>>>>> +       enum ravb_chip_id chip_id;
>>>>>> +       int num_tx_desc;
>>>>>
>>>>> Why not "unsigned int"? ...
>>>>> This comment applies to a few more subsequent patches.
>>>>
>>>> To avoid signed and unsigned comparison warnings.
>>>>
>>>>>
>>>>>> +};
>>>>>> +
>>>>>>  struct ravb_private {
>>>>>>         struct net_device *ndev;
>>>>>>         struct platform_device *pdev; @@ -1040,6 +1045,8 @@
>>>>>> struct ravb_private {
>>>>>>         unsigned txcidm:1;              /* TX Clock Internal Delay
>>> Mode
>>>>> */
>>>>>>         unsigned rgmii_override:1;      /* Deprecated rgmii-*id
>>> behavior
>>>>> */
>>>>>>         int num_tx_desc;                /* TX descriptors per
>> packet
>>> */
>>>>>
>>>>> ... oh, here's the original culprit.
>>>>
>>>> Exactly, this the reason.
>>>>
>>>> Do you want me to change this into unsigned int? Please let me know.
>>>
>>> Up to you (or the maintainer? ;-)
>>>
>>> For new fields (in the other patches), I would use unsigned for all
>>> unsigned values.  Signed values have more pitfalls related to
>>> undefined behavior.
>>
>> Sergei, What is your thoughts here? Please let me know.
> 
> Here is my plan.
> 
> I will split this patch into two as Andrew suggested and 

   If you mran changing the ravb_private::num_tx_desc to *unsigned*, it'll be
a good cleanup. What's would be the 2nd part tho?

> Then on the second patch will add as info->unaligned_tx as Sergei suggested.

   OK.

> Now the only open point is related to the data type of "int num_tx_desc"
> and to align with sh_eth driver I will keep int.

   The sh_eth driver simply doesn't have this -- it always use 1 descriptor.

> Regards,
> Biju

MBR, Sergey