[bug report] net: macb: convert to phylink

[Dan Carpenter <error27@gmail.com>]

Hello Antoine Tenart,

The patch 7897b071ac3b: "net: macb: convert to phylink" from Nov 13,
2019, leads to the following Smatch static checker warning:

	drivers/clk/clk.c:133 clk_prepare_lock()
	warn: sleeping in atomic context

drivers/clk/clk.c
    126 static void clk_prepare_lock(void)
    127 {
    128         if (!mutex_trylock(&prepare_lock)) {
    129                 if (prepare_owner == current) {
    130                         prepare_refcnt++;
    131                         return;
    132                 }
--> 133                 mutex_lock(&prepare_lock);
    134         }
    135         WARN_ON_ONCE(prepare_owner != NULL);
    136         WARN_ON_ONCE(prepare_refcnt != 0);
    137         prepare_owner = current;
    138         prepare_refcnt = 1;
    139 }

The problem is that cadence/macb_main calls clk_set_rate() while holding
a spinlock.

The call tree is:

owl_uart_set_termios() <- disables preempt
-> owl_uart_change_baudrate()
rda_uart_set_termios() <- disables preempt
-> rda_uart_change_baudrate()
atmel_set_termios() <- disables preempt
macb_mac_link_up() <- disables preempt  (THIS ONE)
-> macb_set_tx_clk()
   -> clk_set_rate()
      -> clk_prepare_lock()

drivers/net/ethernet/cadence/macb_main.c
   666  static void macb_mac_link_up(struct phylink_config *config,
   667                               struct phy_device *phy,
   668                               unsigned int mode, phy_interface_t interface,
   669                               int speed, int duplex,
   670                               bool tx_pause, bool rx_pause)
   671  {
   672          struct net_device *ndev = to_net_dev(config->dev);
   673          struct macb *bp = netdev_priv(ndev);
   674          struct macb_queue *queue;
   675          unsigned long flags;
   676          unsigned int q;
   677          u32 ctrl;
   678  
   679          spin_lock_irqsave(&bp->lock, flags);
                ^^^^^^^^^^^^^^^^^
Spin lock.

   680  
   681          ctrl = macb_or_gem_readl(bp, NCFGR);
   682  
   683          ctrl &= ~(MACB_BIT(SPD) | MACB_BIT(FD));
   684  
   685          if (speed == SPEED_100)
   686                  ctrl |= MACB_BIT(SPD);
   687  
   688          if (duplex)
   689                  ctrl |= MACB_BIT(FD);
   690  
   691          if (!(bp->caps & MACB_CAPS_MACB_IS_EMAC)) {
   692                  ctrl &= ~MACB_BIT(PAE);
   693                  if (macb_is_gem(bp)) {
   694                          ctrl &= ~GEM_BIT(GBE);
   695  
   696                          if (speed == SPEED_1000)
   697                                  ctrl |= GEM_BIT(GBE);
   698                  }
   699  
   700                  if (rx_pause)
   701                          ctrl |= MACB_BIT(PAE);
   702  
   703                  macb_set_tx_clk(bp, speed);
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^
Takes a mutex.

   704  
   705                  /* Initialize rings & buffers as clearing MACB_BIT(TE) in link down
   706                   * cleared the pipeline and control registers.
   707                   */
   708                  bp->macbgem_ops.mog_init_rings(bp);
   709                  macb_init_buffers(bp);

regards,
dan carpenter