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Date:   Mon, 14 Aug 2023 13:02:31 +0530
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Subject: Re: [PATCH v3 3/5] net: ti: icss-iep: Add IEP driver
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To:     Andrew Davis <afd@ti.com>, MD Danish Anwar <danishanwar@ti.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Roger Quadros <rogerq@kernel.org>,
        Simon Horman <simon.horman@corigine.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Andrew Lunn <andrew@lunn.ch>,
        Richard Cochran <richardcochran@gmail.com>,
        Conor Dooley <conor+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>
CC:     <nm@ti.com>, <srk@ti.com>, <linux-kernel@vger.kernel.org>,
        <devicetree@vger.kernel.org>, <netdev@vger.kernel.org>,
        <linux-omap@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
References: <20230809114906.21866-1-danishanwar@ti.com>
 <20230809114906.21866-4-danishanwar@ti.com>
 <b43ee5ca-2aab-445a-e24b-cbc95f9186ea@ti.com>
 <c7ddb12d-ae18-5fc2-9729-c88ea73b21d7@ti.com>
 <4c40fbe4-3492-ec76-e452-3a3ecb0f2433@ti.com>
From:   Md Danish Anwar <a0501179@ti.com>
Organization: Texas Instruments
In-Reply-To: <4c40fbe4-3492-ec76-e452-3a3ecb0f2433@ti.com>
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On 11/08/23 8:54 pm, Andrew Davis wrote:
> On 8/10/23 6:50 AM, 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@ti.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@ti.com>
>>>> Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
>>>> Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
>>>> Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
>>>> Signed-off-by: MD Danish Anwar <danishanwar@ti.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.
>>
> 
> Sounds like you only need direct register access for time sensitive
> gettime/settime functions, if that is the only place writel()/readl() is
> needed just drop the helper and use directly in that one spot.
> 

In total both icss_iep_readl() and writel() are used 4 time each. All related
to gettime / settime. This is the only place where these helper APIs are used.
I will drop these helper apis and used readl / writel directly.

>>>
>>> [...]
>>>
>>>> +static void icss_iep_enable(struct icss_iep *iep)
>>>> +{
>>>> +    regmap_update_bits(iep->map, ICSS_IEP_GLOBAL_CFG_REG,
>>>> +               IEP_GLOBAL_CFG_CNT_ENABLE,
>>>> +               IEP_GLOBAL_CFG_CNT_ENABLE);
>>>
>>> Have you looked into regmap_fields?
>>>
>>
>> No I hadn't. But now I looked into regmap_fields, seems to be another way to
>> update the bits, instead of passing mask and value, regmap_filed_read / write
>> only takes the value. But for that we will need to create a regmap field. If
>> you want me to switch to regmap_fields instead of regmap_update_bits I can make
>> the changes. But I am fine with regmap_update_bits().
>>
> 
> I'm suggesting regmap fields as I have used it several times and it resulted
> in greatly improved readability. Yes you will need a regmap field table, but
> that is the best part, it lets you put all your bit definitions in one spot
> that can match 1:1 with the datasheet, much easier to check for correctness
> than if the bit usages are all spread out in the driver.
> 
> I won't insist on you converting this driver to use it today, but I do recommend
> you at least give it a shot for your own learning.
> 

Sure Andrew. For now I will keep it as regmap_update_bits(). I will look into
regmap_fields for my own learning.

> Andrew
> 
>>> [...]
>>>
>>>> +
>>>> +    if (!!(iep->latch_enable & BIT(index)) == !!on)
>>>> +        goto exit;
>>>> +
>>>
>>> There has to be a better way to write this logic..
>>>
>>> [...]
>>>
>>>> +
>>>> +static const struct of_device_id icss_iep_of_match[];
>>>> +
>>>
>>> Why the forward declaration?
>>
>> I will remove this, I don't see any reason for this.
>>
>>>
>>>> +static int icss_iep_probe(struct platform_device *pdev)
>>>> +{
>>>> +    struct device *dev = &pdev->dev;
>>>> +    struct icss_iep *iep;
>>>> +    struct clk *iep_clk;
>>>> +
>>>> +    iep = devm_kzalloc(dev, sizeof(*iep), GFP_KERNEL);
>>>> +    if (!iep)
>>>> +        return -ENOMEM;
>>>> +
>>>> +    iep->dev = dev;
>>>> +    iep->base = devm_platform_ioremap_resource(pdev, 0);
>>>> +    if (IS_ERR(iep->base))
>>>> +        return -ENODEV;
>>>> +
>>>> +    iep_clk = devm_clk_get(dev, NULL);
>>>> +    if (IS_ERR(iep_clk))
>>>> +        return PTR_ERR(iep_clk);
>>>> +
>>>> +    iep->refclk_freq = clk_get_rate(iep_clk);
>>>> +
>>>> +    iep->def_inc = NSEC_PER_SEC / iep->refclk_freq;    /* ns per clock
>>>> tick */
>>>> +    if (iep->def_inc > IEP_MAX_DEF_INC) {
>>>> +        dev_err(dev, "Failed to set def_inc %d.  IEP_clock is too slow to be
>>>> supported\n",
>>>> +            iep->def_inc);
>>>> +        return -EINVAL;
>>>> +    }
>>>> +
>>>> +    iep->plat_data = of_device_get_match_data(dev);
>>>
>>> Directly using of_*() functions is often wrong, try just
>>> device_get_match_data().
>>>
>>
>> Sure. I will change to device_get_match_data().
>>
>>> [...]
>>>
>>>> +static struct platform_driver icss_iep_driver = {
>>>> +    .driver = {
>>>> +        .name = "icss-iep",
>>>> +        .of_match_table = of_match_ptr(icss_iep_of_match),
>>>
>>> This driver cannot work without OF, using of_match_ptr() is not needed.
>>>
>>
>> Sure, I will drop of_match_ptr().
>>
>>> Andrew
>>
>>
>> For reading and updating registers, we can have
>>     1. icss_iep_readl / writel and regmap_update_bits() OR
>>     2. regmap_read / write and regmap_update_bits() OR
>>     3. icss_iep_readl / writel and regmap_fields OR
>>     4. regmap_read / write and regmap_fields
>>     
>>
>> Currently we are using 1. Please let me know if you are fine with this and I
>> can continue using 1. If not, please let me know your recommendation out of
>> this 4.
>>
>> [1]
>> https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/commit/?h=linux-5.10.y&id=f4f45bf71cad5be232536d63a0557d13a7eed162
>>

-- 
Thanks and Regards,
Danish.