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

[Md Danish Anwar <a0501179@ti.com>]

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.

> 
> [...]
> 
>> +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().

> [...]
> 
>> +
>> +    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.

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