netdev - Re: [PATCH net-next v3 1/6] net: phy: mscc: migrate to phy_select/restore

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Date:   Mon, 19 Nov 2018 15:57:17 +0100
From:   Andreas Schwab <schwab@...e.de>
To:     Quentin Schulz <quentin.schulz@...tlin.com>
Cc:     davem@...emloft.net, andrew@...n.ch, f.fainelli@...il.com,
        allan.nielsen@...rochip.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, thomas.petazzoni@...tlin.com,
        alexandre.belloni@...tlin.com, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH net-next v3 1/6] net: phy: mscc: migrate to phy_select/restore_page functions

On Okt 08 2018, Quentin Schulz <quentin.schulz@...tlin.com> wrote:

> The Microsemi PHYs have multiple banks of registers (called pages).
> Registers can only be accessed from one page, if we need a register from
> another page, we need to switch the page and the registers of all other
> pages are not accessible anymore.
>
> Basically, to read register 5 from page 0, 1, 2, etc., you do the same
> phy_read(phydev, 5); but you need to set the desired page beforehand.
>
> In order to guarantee that two concurrent functions do not change the
> page, we need to do some locking per page. This can be achieved with the
> use of phy_select_page and phy_restore_page functions but phy_write/read
> calls in-between those two functions shall be replaced by their
> lock-free alternative __phy_write/read.
>
> Let's migrate this driver to those functions.

This has some serious locking problem.

[<0>] __schedule+0x25e/0x74c
[<0>] schedule+0x1a/0x58
[<0>] schedule_preempt_disabled+0xc/0x14
[<0>] __mutex_lock.isra.0+0x10e/0x22e
[<0>] __mutex_lock_slowpath+0xe/0x16
[<0>] mutex_lock+0x22/0x2a
[<0>] mdiobus_read+0x36/0x60
[<0>] vsc85xx_config_init+0x4c/0x1e2
[<0>] phy_init_hw+0x3c/0x52
[<0>] phy_attach_direct+0xec/0x1dc
[<0>] phy_connect_direct+0x1a/0x56
[<0>] macb_probe+0x800/0xb5e [macb]
[<0>] platform_drv_probe+0x3e/0x7e
[<0>] really_probe+0xba/0x310
[<0>] driver_probe_device+0x54/0xf2
[<0>] __driver_attach+0xde/0x106
[<0>] bus_for_each_dev+0x4a/0x72
[<0>] driver_attach+0x1a/0x22
[<0>] bus_add_driver+0x1ce/0x212
[<0>] driver_register+0x3a/0xd0
[<0>] __platform_driver_register+0x3a/0x42
[<0>] macb_driver_init+0x20/0x28 [macb]
[<0>] do_one_initcall+0x48/0x128
[<0>] do_init_module+0x4a/0x186
[<0>] load_module+0xd6a/0xe6a
[<0>] sys_finit_module+0xc6/0xfc
[<0>] check_syscall_nr+0x22/0x22

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@...e.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."