netdev - Re: [PATCH v3 net-next 13/19] ionic: Add initial ethtool support

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Message-ID: <5a131da9-d7cf-a477-e622-783f14c8e385@pensando.io>
Date:   Thu, 18 Jul 2019 10:54:27 -0700
From:   Shannon Nelson <snelson@...sando.io>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH v3 net-next 13/19] ionic: Add initial ethtool support

On 7/18/19 10:28 AM, Andrew Lunn wrote:
> On Thu, Jul 18, 2019 at 10:05:23AM -0700, Shannon Nelson wrote:
>> On 7/17/19 8:21 PM, Andrew Lunn wrote:
>>> On Tue, Jul 09, 2019 at 03:42:39PM -0700, Shannon Nelson wrote:
>>>> On 7/8/19 7:27 PM, Andrew Lunn wrote:
>>>>>> +static int ionic_get_module_eeprom(struct net_device *netdev,
>>>>>> +				   struct ethtool_eeprom *ee,
>>>>>> +				   u8 *data)
>>>>>> +{
>>>>>> +	struct lif *lif = netdev_priv(netdev);
>>>>>> +	struct ionic_dev *idev = &lif->ionic->idev;
>>>>>> +	struct xcvr_status *xcvr;
>>>>>> +	u32 len;
>>>>>> +
>>>>>> +	/* copy the module bytes into data */
>>>>>> +	xcvr = &idev->port_info->status.xcvr;
>>>>>> +	len = min_t(u32, sizeof(xcvr->sprom), ee->len);
>>>>>> +	memcpy(data, xcvr->sprom, len);
>>>>> Hi Shannon
>>>>>
>>>>> This also looks odd. Where is the call into the firmware to get the
>>>>> eeprom contents? Even though it is called 'eeprom', the data is not
>>>>> static. It contains real time diagnostic values, temperature, transmit
>>>>> power, receiver power, voltages etc.
>>>> idev->port_info is a memory mapped space that the device keeps up-to-date.
>>> Hi Shannon
>>>
>>> It at least needs a comment. How frequently does the device update
>>> this chunk of memory? It would be good to comment about that as
>>> well. Or do MMIO reads block while i2c operations occur to update the
>>> memory?
>> The device keeps this updated when changes happen internally so that there
>> is no need to block on MMIO read.
> Hi Shannon
>
> I'm thinking about the diagnostic page. RX and TX power, temperature,
> alarms etc. These are real time values, so you should read them on
> demand, or at last only cache them for a short time.
>
>

They *are* read on demand.  The port_info and lif_info structs are dma 
mapped spaces that the device keeps up-to-date with PCI writes in the 
background so that the driver can do a quick memory read for current data.

sln