linux-kernel - Re: [PATCH net-next v3 2/6] net: phy: microchip_t1s: replace read-modify-write code with phy_modify

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Message-ID: <ZG9599nfDnkcw8er@debian>
Date:   Thu, 25 May 2023 17:08:39 +0200
From:   Ramón Nordin Rodriguez 
        <ramon.nordin.rodriguez@...roamp.se>
To:     Parthiban Veerasooran <Parthiban.Veerasooran@...rochip.com>
Cc:     andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, horatiu.vultur@...rochip.com,
        Woojung.Huh@...rochip.com, Nicolas.Ferre@...rochip.com,
        Thorsten.Kummermehr@...rochip.com
Subject: Re: [PATCH net-next v3 2/6] net: phy: microchip_t1s: replace
 read-modify-write code with phy_modify_mmd

On Wed, May 24, 2023 at 08:15:35PM +0530, Parthiban Veerasooran wrote:
> Replace read-modify-write code in the lan867x_config_init function to
> avoid handling data type mismatch and to simplify the code.
> 
> Signed-off-by: Parthiban Veerasooran <Parthiban.Veerasooran@...rochip.com>
> ---
>  drivers/net/phy/microchip_t1s.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/phy/microchip_t1s.c b/drivers/net/phy/microchip_t1s.c
> index a42a6bb6e3bd..b5b5a95fa6e7 100644
> --- a/drivers/net/phy/microchip_t1s.c
> +++ b/drivers/net/phy/microchip_t1s.c
> @@ -31,19 +31,19 @@
>   * W   0x1F 0x0099 0x7F80 ------
>   */
>  
> -static const int lan867x_fixup_registers[12] = {
> +static const u32 lan867x_fixup_registers[12] = {
>  	0x00D0, 0x00D1, 0x0084, 0x0085,
>  	0x008A, 0x0087, 0x0088, 0x008B,
>  	0x0080, 0x00F1, 0x0096, 0x0099,
>  };
>  
> -static const int lan867x_fixup_values[12] = {
> +static const u16 lan867x_fixup_values[12] = {
>  	0x0002, 0x0000, 0x3380, 0x0006,
>  	0xC000, 0x801C, 0x033F, 0x0404,
>  	0x0600, 0x2400, 0x2000, 0x7F80,
>  };
>  
> -static const int lan867x_fixup_masks[12] = {
> +static const u16 lan867x_fixup_masks[12] = {
>  	0x0E03, 0x0300, 0xFFC0, 0x000F,
>  	0xF800, 0x801C, 0x1FFF, 0xFFFF,
>  	0x0600, 0x7F00, 0x2000, 0xFFFF,
> @@ -63,23 +63,22 @@ static int lan867x_config_init(struct phy_device *phydev)
>  	 * used, which might then write the same value back as read + modified.
>  	 */
>  
> -	int reg_value;
>  	int err;
> -	int reg;
>  
>  	/* Read-Modified Write Pseudocode (from AN1699)
>  	 * current_val = read_register(mmd, addr) // Read current register value
>  	 * new_val = current_val AND (NOT mask) // Clear bit fields to be written
>  	 * new_val = new_val OR value // Set bits
> -	 * write_register(mmd, addr, new_val) // Write back updated register value
> +	 * write_register(mmd, addr, new_val) // Write back updated register value.
> +	 * Although AN1699 says Read, Modify, Write, the write is not required if
> +	 * the register already has the required value.
>  	 */

Nitpick, I think this block comment can be reduced to:
/* The following block deviates from AN1699 which states that a values
 * should be written back, even if unmodified.
 * Which is not necessary, so it's safe to use phy_modify_mmd here.*/

 The comment I added was intended to describe why I was doing weird
 things, but now I think it's more interesting to describe why we're
 deviating from the AN.

 Or the block comment could be dropped all togheter, I'm guessing no one
 is going to consult the AN if things 'just work'

>  	for (int i = 0; i < ARRAY_SIZE(lan867x_fixup_registers); i++) {
> -		reg = lan867x_fixup_registers[i];
> -		reg_value = phy_read_mmd(phydev, MDIO_MMD_VEND2, reg);
> -		reg_value &= ~lan867x_fixup_masks[i];
> -		reg_value |= lan867x_fixup_values[i];
> -		err = phy_write_mmd(phydev, MDIO_MMD_VEND2, reg, reg_value);
> -		if (err != 0)
> +		err = phy_modify_mmd(phydev, MDIO_MMD_VEND2,
> +				     lan867x_fixup_registers[i],
> +				     lan867x_fixup_masks[i],
> +				     lan867x_fixup_values[i]);
> +		if (err)
>  			return err;
>  	}
>  
> -- 
> 2.34.1
>