linux-kernel - Re: [PATCH v3 3/5] net: ti: icss-iep: Add IEP driver

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Message-ID: <80071066-bec4-c2dd-8ad3-932e8d9e27c1@ti.com>
Date:   Thu, 10 Aug 2023 17:41:43 +0530
From:   Md Danish Anwar <a0501179@...com>
To:     Roger Quadros <rogerq@...nel.org>, Andrew Davis <afd@...com>,
        MD Danish Anwar <danishanwar@...com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Simon Horman <simon.horman@...igine.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Andrew Lunn <andrew@...n.ch>,
        Richard Cochran <richardcochran@...il.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
CC:     <nm@...com>, <srk@...com>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-omap@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 3/5] net: ti: icss-iep: Add IEP driver

On 10/08/23 5:35 pm, Roger Quadros wrote:
> 
> 
> On 10/08/2023 14:50, Md Danish Anwar wrote:
>> Hi Andrew,
>>
>> On 09/08/23 8:30 pm, Andrew Davis wrote:
>>> On 8/9/23 6:49 AM, MD Danish Anwar wrote:
>>>> From: Roger Quadros <rogerq@...com>
>>>>
>>>> Add a driver for Industrial Ethernet Peripheral (IEP) block of PRUSS to
>>>> support timestamping of ethernet packets and thus support PTP and PPS
>>>> for PRU ethernet ports.
>>>>
>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>> Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
>>>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>>>> Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
>>>> Signed-off-by: MD Danish Anwar <danishanwar@...com>
>>>> ---
>>>>   drivers/net/ethernet/ti/Kconfig          |  12 +
>>>>   drivers/net/ethernet/ti/Makefile         |   1 +
>>>>   drivers/net/ethernet/ti/icssg/icss_iep.c | 935 +++++++++++++++++++++++
>>>>   drivers/net/ethernet/ti/icssg/icss_iep.h |  38 +
>>>>   4 files changed, 986 insertions(+)
>>>>   create mode 100644 drivers/net/ethernet/ti/icssg/icss_iep.c
>>>>   create mode 100644 drivers/net/ethernet/ti/icssg/icss_iep.h
>>>>
>>>> diff --git a/drivers/net/ethernet/ti/Kconfig b/drivers/net/ethernet/ti/Kconfig
>>>> index 63e510b6860f..88b5b1b47779 100644
>>>> --- a/drivers/net/ethernet/ti/Kconfig
>>>> +++ b/drivers/net/ethernet/ti/Kconfig
>>>> @@ -186,6 +186,7 @@ config CPMAC
>>>>   config TI_ICSSG_PRUETH
>>>>       tristate "TI Gigabit PRU Ethernet driver"
>>>>       select PHYLIB
>>>> +    select TI_ICSS_IEP
>>>
>>> Why not save selecting this until you add its use in the ICSSG_PRUETH driver in
>>> the next patch.
>>>
>>
>> The next patch is only adding changes to icssg-prueth .c /.h files. This patch
>> is adding changes to Kconfig and the Makefile. To keep it that way selecting
>> this is added in this patch. No worries, I will move this to next patch.
>>
>>> [...]
>>>
>>>> +
>>>> +static u32 icss_iep_readl(struct icss_iep *iep, int reg)
>>>> +{
>>>> +    return readl(iep->base + iep->plat_data->reg_offs[reg]);
>>>> +}
>>>
>>> Do these one line functions really add anything? Actually why
>>> not use the regmap you have here.
>>
>> These one line functions are not really adding anything but they are acting as
>> a wrapper around readl /writel and providing some sort of encapsulation as
>> directly calling readl will result in a little complicated code.
>>
>> /* WIth One line function */
>> ts_lo = icss_iep_readl(iep, ICSS_IEP_COUNT_REG0);
>>
>> /* Without one line function */
>> ts_lo = readl(iep->base, iep->plat_data->reg_offs[ICSS_IEP_COUNT_REG0]);
>>
>> Previously regmap was used in this driver. But in older commit [1] in
>> 5.10-ti-linux-kernel (Before I picked the driver for upstream) it got changed
>> to readl / writel stating that regmap_read / write is too slow. IEP is time
>> sensitive and needs faster read and write, probably because of this they
>> changed it.
> 
> This is true. Can you please pick the exact reasoning mentioned there
> and put it as a comment where you use read/writel() instead of regmap()
> so we don't forget this and accidentally switch it back to regmap()
> in the future.
> 

Sure I can add this comment wherever we use readl / writel().

> I think this is only required for read/write to the IEP count register and
> SYNC_CTRL_REG when doing gettime/settime.
> 

Yes. This is only used in SYNC_CTRL_REG and IEP counters.

-- 
Thanks and Regards,
Danish.