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

    >>
    >> [...]
    >>
    >>> +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.

    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
    >

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