Re: [RESEND PATCH 2/2] misc: add support for retimers interfaces on Intel MAX 10 BMC

On Thu, Jan 07, 2021 at 02:07:08PM +0800, Xu Yilun wrote:

This driver supports the ethernet retimers (C827) for the Intel PAC
(Programmable Acceleration Card) N3000, which is a FPGA based Smart NIC.

C827 is an Intel(R) Ethernet serdes transceiver chip that supports
up to 100G transfer. On Intel PAC N3000 there are 2 C827 chips
managed by the Intel MAX 10 BMC firmware. They are configured in 4 ports
10G/25G retimer mode. Host could query their link states and firmware
version information via retimer interfaces (Shared registers) on Intel
MAX 10 BMC. The driver creates sysfs interfaces for users to query these
information.

Networking people, please look at this sysfs file:

+What:		/sys/bus/platform/devices/n3000bmc-retimer.*.auto/link_statusX
+Date:		Jan 2021
+KernelVersion:	5.12
+Contact:	Xu Yilun [off-list ref]
+Description:	Read only. Returns the status of each line side link. "1" for
+		link up, "0" for link down.
+		Format: "%u".

as I need your approval to add it because it is not the "normal" way for
link status to be exported to userspace.

One code issue:

+#define to_link_attr(dev_attr) \
+	container_of(dev_attr, struct link_attr, attr)
+
+static ssize_t
+link_status_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct m10bmc_retimer *retimer = dev_get_drvdata(dev);
+	struct link_attr *lattr = to_link_attr(attr);
+	unsigned int val;
+	int ret;
+
+	ret = m10bmc_sys_read(retimer->m10bmc, M10BMC_PKVL_LSTATUS, &val);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%u\n",
+			  !!(val & BIT((retimer->id << 2) + lattr->index)));
+}
+
+#define link_status_attr(_index)				\
+	static struct link_attr link_attr_status##_index =	\
+		{ .attr = __ATTR(link_status##_index, 0444,	\
+				 link_status_show, NULL),	\
+		  .index = (_index) }

Why is this a "raw" attribute and not a device attribute?

Please just use a normal DEVICE_ATTR_RO() macro to make it simpler and
easier to understand over time, what you are doing here.  I can't
determine what is happening with this code now...

thanks,

greg k-h