[PATCH v3 net] net: stmmac: dwmac4: extend timeout for VLAN Tag register busy bit check

[Serge Semin]

Hi Shenwei

On Mon, Sep 23, 2024 at 03:26:02PM -0500, Shenwei Wang wrote:
> Increase the timeout for checking the busy bit of the VLAN Tag register
> from 10µs to 500ms. This change is necessary to accommodate scenarios
> where Energy Efficient Ethernet (EEE) is enabled.
> 
> Overnight testing revealed that when EEE is active, the busy bit can
> remain set for up to approximately 300ms. The new 500ms timeout provides
> a safety margin.
> 
> Fixes: ed64639bc1e0 ("net: stmmac: Add support for VLAN Rx filtering")
> Signed-off-by: Shenwei Wang <shenwei.wang at nxp.com>
> Reviewed-by: Andrew Lunn <andrew at lunn.ch>

> Reviewed-by: Serge Semin <fancer.lancer at gmail.com>

Please note, you can't add the R-b tag without explicitly getting one
from the reviewer/maintainer/etc. Please read the chapter
"When to use Acked-by:, Cc:, and Co-developed-by:" in
Documentation/process/submitting-patches.rst

> ---
> Changes in V3:
>  - re-org the error-check flow per Serge's review.
> 
> Changes in v2:
>  - replace the udelay with readl_poll_timeout per Simon's review.
> 
> ---
>  .../net/ethernet/stmicro/stmmac/dwmac4_core.c  | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> index a1858f083eef..0d27dd71b43e 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> @@ -14,6 +14,7 @@
>  #include <linux/slab.h>
>  #include <linux/ethtool.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include "stmmac.h"
>  #include "stmmac_pcs.h"
>  #include "dwmac4.h"
> @@ -471,7 +472,7 @@ static int dwmac4_write_vlan_filter(struct net_device *dev,
>  				    u8 index, u32 data)
>  {
>  	void __iomem *ioaddr = (void __iomem *)dev->base_addr;
> -	int i, timeout = 10;
> +	int ret;
>  	u32 val;
> 
>  	if (index >= hw->num_vlan)
> @@ -487,16 +488,15 @@ static int dwmac4_write_vlan_filter(struct net_device *dev,
> 
>  	writel(val, ioaddr + GMAC_VLAN_TAG);
> 
> -	for (i = 0; i < timeout; i++) {
> -		val = readl(ioaddr + GMAC_VLAN_TAG);
> -		if (!(val & GMAC_VLAN_TAG_CTRL_OB))
> -			return 0;
> -		udelay(1);

> +	ret = readl_poll_timeout(ioaddr + GMAC_VLAN_TAG, val,
> +				 !(val & GMAC_VLAN_TAG_CTRL_OB),
> +				 1000, 500000); //Timeout 500ms

Please drop the comment at the end of the statement. First of all the
C++-style comments are discouraged to be used in the kernel code except
when in the block of the SPDX licence identifier, or when documenting
structs in headers. Secondly the tail-comments are discouraged either
(see Documentation/process/maintainer-tip.rst - yes, it's for
tip-tree, but the rule see informally applicable for the entire
kernel). Thirdly the comment is pointless here since the literal
500000 means exactly that.

-Serge(y)

> +	if (ret) {
> +		netdev_err(dev, "Timeout accessing MAC_VLAN_Tag_Filter\n");
> +		return -EBUSY;
>  	}
> 
> -	netdev_err(dev, "Timeout accessing MAC_VLAN_Tag_Filter\n");
> -
> -	return -EBUSY;
> +	return 0;
>  }
> 
>  static int dwmac4_add_hw_vlan_rx_fltr(struct net_device *dev,
> --
> 2.34.1
>