Re: [PATCH V3 1/4 net] net: dsa: b53: deal with Northstar devices using CPU port 5 or 7
From: Jonas Gorski <jonas.gorski@gmail.com>
Date: 2026-08-18 11:46:23
Also in:
linux-arm-kernel, linux-devicetree
Hi, On Wed, Aug 12, 2026 at 3:28 PM Rafał Miłecki [off-list ref] wrote:
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From: Rafał Miłecki <rafal@milecki.pl> Northstar devices have 3 CPU ports. Ports 5 and 7 may be used but have their limitations. Warn user when CPU port 8 isn't used and add EAP setup workaround to avoid non-functional standalone ports. Fixes: 4227ea91e265 ("net: dsa: b53: prevent standalone from trying to forward to other ports") Cc: Semih Baskan <redacted> Signed-off-by: Rafał Miłecki <rafal@milecki.pl> Tested-by: Semih Baskan <redacted> --- This fixes a regression so it's a net.git material V2: Print warning on switch setup instead of on actual EAP mode change V3: Proper subject prefix & shorter comments (long one comes with 2/2) drivers/net/dsa/b53/b53_common.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c index 3f5b9592794d..5fd8362d0430 100644 --- a/drivers/net/dsa/b53/b53_common.c +++ b/drivers/net/dsa/b53/b53_common.c@@ -332,6 +332,14 @@ static void b53_set_eap_mode(struct b53_device *dev, int port, int mode) { u64 eap_conf; + /* + * On Northstar setting EAP_MODE_SIMPLIFIED with CPU port 5/7 breaks
This isn't just northstar, this is any dual IMP capable switch
+ * standalone ports, see: + * https://lore.kernel.org/netdev/ce4d9b7b-aaf6-4796-94fb-8c3d6a1dcd4d@gmail.com/ (local) + */ + if (is5301x(dev) && !dsa_is_cpu_port(dev->ds, B53_CPU_PORT)) + return;
This should be moved below the 5325/5365 check and just !dsa_is_cpu_port(dev->ds, B53_CPU_PORT))
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+ if (is5325(dev) || is5365(dev) || dev->chip_id == BCM5389_DEVICE_ID) return;@@ -1281,6 +1289,10 @@ static int b53_setup(struct dsa_switch *ds) u16 pvid; int ret; + /* Discourage users from using port 5 or 7 due to limited features */ + if (is5301x(dev) && !dsa_is_cpu_port(dev->ds, B53_CPU_PORT))
This should be if (!is5325(dev) && !is5365(dev) && !dsa_is_cpu_port(dev->ds, B53_CPU_PORT)) dual IMP mode is also supported by external switches (e.g. bcm53115 and bcm53125), and if for some reason someone would try to use port 5 only on these you will have the same issues.
+ dev_warn(dev->dev, "switch to CPU port 8 to use all switch features\n");
I think this warning is too mild; it should be something like "Using port 5 or 7 as CPU port is not a valid configuration and will prevent the switch from working properly..\n" Best regards, Jonas