netdev - Re: [PATCH net-next] net: bgmac: support MDIO described in DT

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Message-ID: <79c91b0e-7f6a-ef40-9ab2-ee8212bf5791@gmail.com>
Date:   Mon, 20 Sep 2021 19:57:06 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH net-next] net: bgmac: support MDIO described in DT

On 20.09.2021 18:11, Florian Fainelli wrote:
> On 9/20/21 5:34 AM, Rafał Miłecki wrote:
>> From: Rafał Miłecki <rafal@...ecki.pl>
>>
>> Check ethernet controller DT node for "mdio" subnode and use it with
>> of_mdiobus_register() when present. That allows specifying MDIO and its
>> PHY devices in a standard DT based way.
>>
>> This is required for BCM53573 SoC support which has an MDIO attached
>> switch.
>>
>> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
>> ---
>>   drivers/net/ethernet/broadcom/bgmac-bcma-mdio.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/broadcom/bgmac-bcma-mdio.c b/drivers/net/ethernet/broadcom/bgmac-bcma-mdio.c
>> index 6ce80cbcb48e..086739e4f40a 100644
>> --- a/drivers/net/ethernet/broadcom/bgmac-bcma-mdio.c
>> +++ b/drivers/net/ethernet/broadcom/bgmac-bcma-mdio.c
>> @@ -10,6 +10,7 @@
>>   
>>   #include <linux/bcma/bcma.h>
>>   #include <linux/brcmphy.h>
>> +#include <linux/of_mdio.h>
>>   #include "bgmac.h"
>>   
>>   static bool bcma_mdio_wait_value(struct bcma_device *core, u16 reg, u32 mask,
>> @@ -211,6 +212,7 @@ struct mii_bus *bcma_mdio_mii_register(struct bgmac *bgmac)
>>   {
>>   	struct bcma_device *core = bgmac->bcma.core;
>>   	struct mii_bus *mii_bus;
>> +	struct device_node *np;
>>   	int err;
>>   
>>   	mii_bus = mdiobus_alloc();
>> @@ -229,7 +231,9 @@ struct mii_bus *bcma_mdio_mii_register(struct bgmac *bgmac)
>>   	mii_bus->parent = &core->dev;
>>   	mii_bus->phy_mask = ~(1 << bgmac->phyaddr);
>>   
>> -	err = mdiobus_register(mii_bus);
>> +	np = of_get_child_by_name(core->dev.of_node, "mdio");
> 
> I believe this leaks np and the use case is not exactly clear to me
> here. AFAICT the Northstar SoCs have two MDIO controllers: one for
> internal PHYs and one for external PHYs which how you would attach a
> switch to the chip (in chipcommonA). Is 53573 somewhat different here?
> What is the MDIO bus driver that is being used?

of_get_child_by_name() doesn't seem to increase refcount or anything and
I think it's how most drivers handle it. I don't think it should leak.

BCM53573 is a built with some older blocks. Please check:

4ebd50472899 ("ARM: BCM53573: Initial support for Broadcom BCM53573 SoCs")
     BCM53573 series is a new family with embedded wireless. By marketing
     people it's sometimes called Northstar but it uses different CPU and has
     different architecture so we need a new symbol for it.
     Fortunately it shares some peripherals with other iProc based SoCs so we
     will be able to reuse some drivers/bindings.

e90d2d51c412 ("ARM: BCM5301X: Add basic dts for BCM53573 based Tenda AC9")
     BCM53573 seems to be low priced alternative for Northstar chipsts. It
     uses single core Cortex-A7 and doesn't have SDU or local (TWD) timer. It
     was also stripped out of independent SPI controller and 2 GMACs.

Northstar uses SRAB which is some memory based (0x18007000) access to
switch register space.
BCM53573 uses different blocks & mappings and it doesn't include SRAB at
0x18007000. Accessing switch registers is handled over MDIO.