Subject: Re: RTL 8169 linux driver question

From: Stéphane ANCELOT <[email-masked]>
Date: Wed, 28 Nov 2012 01:35:18 +0100

On 27/11/2012 23:46, Francois Romieu wrote:
> David Laight <[email-masked]> :
>> Stéphane ANCELOT <[email-masked]> :
>>> I had problem with it, my application sends a frame that is immediately
>>> transmitted back by some slaves, there was abnormally 100us  lost
>>> between the send and receive call.
>>>
>>> Finally I found it was coming from the following register setup in the
>>> driver :
>>>
>>> RTL_W16(IntrMitigate, 0x5151);
>>>
>>> Can you give me some details about it, since I do not have the RTL8169
>>> programming guide.
>> That sounds like an 'interrupt mitigation' setting - which will cause
>> RX interrupts to be delayed a short time in order to reduce the
>> interrupt load on the kernel.
>>
>> There is usually an 'ethtool' setting to disable interrupt mitigation.
> Something like the patch below against net-next could help once I will
> have tested it.
>
> I completely guessed the Tx usec scale factor at gigabit speed (125 us,
> 100 us, disabled, who knows ?) and I have no idea which specific chipsets
> it should work with.
using 0x5151 value at 100mb FDX, I know it introduced exactly 100us 
delay (Tx+Rx).

> Hayes, may I expect some hindsight regarding:
> 1 - the availability of the IntrMitigate (0xe2) register through the
>      8169, 8168 and 810x line of chipsets
> 2 - the Tx timer unit at gigabit speed
>
> It would save me some time.*
Hayes, it would have spared myself a lot of time ;-)

Have a look at what is driving this r8169 component :

http://www.youtube.com/watch?v=wj30CeAFwuk&feature=plcp
A question to nic components developers : I do not understand what 
competitive advantage keeping these things like a secret....

These things are mostly boring for people and oem like myself at 
Numalliance.

Regards,
Stephane Ancelot

> diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
> index 248f883..2623b73 100644
> --- a/drivers/net/ethernet/realtek/r8169.c
> +++ b/drivers/net/ethernet/realtek/r8169.c
> @@ -349,6 +349,12 @@ enum rtl_registers {
>   	RxMaxSize	= 0xda,
>   	CPlusCmd	= 0xe0,
>   	IntrMitigate	= 0xe2,
> +
> +#define RTL_COALESCE_MASK	0x0f
> +#define RTL_COALESCE_SHIFT	4
> +#define RTL_COALESCE_T_MAX	(RTL_COALESCE_MASK)
> +#define RTL_COALESCE_FRAME_MAX	(RTL_COALESCE_MASK << 2)
> +
>   	RxDescAddrLow	= 0xe4,
>   	RxDescAddrHigh	= 0xe8,
>   	EarlyTxThres	= 0xec,	/* 8169. Unit of 32 bytes. */
> @@ -1997,10 +2003,121 @@ static void rtl8169_get_strings(struct net_device *dev, u32 stringset, u8 *data)
>   	}
>   }
>   
> +static struct rtl_coalesce_scale {
> +	u32 speed;
> +	/* Rx / Tx */
> +	u16 usecs[2];
> +} rtl_coalesce_info[] = {
> +	{ .speed = SPEED_10,	.usecs = { 8000, 10000 } },
> +	{ .speed = SPEED_100,	.usecs = { 1000,  1000 } },
> +	{ .speed = SPEED_1000,	.usecs = {  125,   125 } }
> +};
> +
> +static struct rtl_coalesce_scale *rtl_coalesce_scale(struct net_device *dev)
> +{
> +	struct ethtool_cmd ecmd;
> +	int rc, i;
> +
> +	rc = rtl8169_get_settings(dev, &ecmd);
> +	if (rc < 0)
> +		return ERR_PTR(rc);
> +
> +	for (i = 0; i < ARRAY_SIZE(rtl_coalesce_info); i++) {
> +		if (ethtool_cmd_speed(&ecmd) == rtl_coalesce_info[i].speed)
> +			return rtl_coalesce_info + i;
> +	}
> +
> +	return ERR_PTR(-EINVAL);
> +}
> +
> +static int rtl_get_coalesce(struct net_device *dev, struct ethtool_coalesce *ec)
> +{
> +	struct rtl8169_private *tp = netdev_priv(dev);
> +	void __iomem *ioaddr = tp->mmio_addr;
> +	struct rtl_coalesce_scale *scale;
> +	struct {
> +		u32 *max_frames;
> +		u32 *usecs;
> +	} coal_settings [] = {
> +		{ &ec->rx_max_coalesced_frames, &ec->rx_coalesce_usecs },
> +		{ &ec->tx_max_coalesced_frames, &ec->tx_coalesce_usecs }
> +	}, *p = coal_settings;
> +	int i;
> +	u16 w;
> +
> +	memset(ec, 0, sizeof(*ec));
> +
> +	for (w = RTL_R16(IntrMitigate); w; w >>= RTL_COALESCE_SHIFT, p++) {
> +		*p->max_frames = (w & RTL_COALESCE_MASK) << 2;
> +		w >>= RTL_COALESCE_SHIFT;
> +		*p->usecs = w & RTL_COALESCE_MASK;
> +	}
> +
> +	/* Except for null parameeters, the meaning of coalescing parameters
> +	 * depends on the link speed.
> +	 */
> +	scale = rtl_coalesce_scale(dev);
> +	if (PTR_ERR(scale) && (p != coal_settings))
> +		return PTR_ERR(scale);
> +
> +	for (i = 0; i < 2; i++) {
> +		p = coal_settings + i;
> +		*p->usecs *= scale->usecs[i];
> +		if (!*p->usecs && !*p->max_frames)
> +			*p->max_frames = 1;
> +	}
> +
> +	return 0;
> +}
> +
> +static int rtl_set_coalesce(struct net_device *dev, struct ethtool_coalesce *ec)
> +{
> +	struct rtl8169_private *tp = netdev_priv(dev);
> +	void __iomem *ioaddr = tp->mmio_addr;
> +	struct rtl_coalesce_scale *scale;
> +	struct {
> +		u32 frames;
> +		u32 usecs;
> +	} coal_settings [] = {
> +		{ ec->rx_max_coalesced_frames, ec->rx_coalesce_usecs },
> +		{ ec->tx_max_coalesced_frames, ec->tx_coalesce_usecs }
> +	}, *p = coal_settings;
> +	int i, rc;
> +	u16 w = 0;
> +
> +	scale = rtl_coalesce_scale(dev);
> +	rc = PTR_ERR(scale);
> +
> +	for (i = 0; i < 2; i++) {
> +		u32 units;
> +
> +		if (!p->usecs && p->frames == 1)
> +			continue;
> +		if (rc < 0)
> +			goto out;
> +
> +		units = p->usecs / scale->usecs[i];
> +		if (units > RTL_COALESCE_T_MAX || p->usecs % scale->usecs[i] ||
> +		    p->frames > RTL_COALESCE_FRAME_MAX || p->frames % 4)
> +			return -EINVAL;
> +
> +		w <<= RTL_COALESCE_SHIFT;
> +		w |= units;
> +		w <<= RTL_COALESCE_SHIFT;
> +		w |= p->frames >> 2;
> +	}
> +
> +	RTL_W16(IntrMitigate, swab16(w));
> +out:
> +	return rc;
> +}
> +
>   static const struct ethtool_ops rtl8169_ethtool_ops = {
>   	.get_drvinfo		= rtl8169_get_drvinfo,
>   	.get_regs_len		= rtl8169_get_regs_len,
>   	.get_link		= ethtool_op_get_link,
> +	.get_coalesce		= rtl_get_coalesce,
> +	.set_coalesce		= rtl_set_coalesce,
>   	.get_settings		= rtl8169_get_settings,
>   	.set_settings		= rtl8169_set_settings,
>   	.get_msglevel		= rtl8169_get_msglevel,