linux-kernel - [PATCH v1] powerpc: low_i2c: change @lock to raw_spinlock

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Date:   Thu, 25 Feb 2021 23:06:23 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Paul Mackerras <paulus@...ba.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Qinglang Miao <miaoqinglang@...wei.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] powerpc: low_i2c: change @lock to raw_spinlock_t

i2c transfers are occurring with local interrupts disabled:

smp_core99_give_timebase()
  local_irq_save();
  smp_core99_cypress_tb_freeze()
    pmac_i2c_xfer()
      kw_i2c_xfer()
        spin_lock_irqsave(&host->lock, flags)

This is a problem because with PREEMPT_RT a spinlock_t can sleep,
causing the system to hang. Convert the spinlock_t to the
non-sleeping raw_spinlock_t.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 arch/powerpc/platforms/powermac/low_i2c.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/platforms/powermac/low_i2c.c b/arch/powerpc/platforms/powermac/low_i2c.c
index f77a59b5c2e1..ba89c95ef290 100644
--- a/arch/powerpc/platforms/powermac/low_i2c.c
+++ b/arch/powerpc/platforms/powermac/low_i2c.c
@@ -116,7 +116,7 @@ struct pmac_i2c_host_kw
 	int			polled;
 	int			result;
 	struct completion	complete;
-	spinlock_t		lock;
+	raw_spinlock_t		lock;
 	struct timer_list	timeout_timer;
 };
 
@@ -346,14 +346,14 @@ static irqreturn_t kw_i2c_irq(int irq, void *dev_id)
 	struct pmac_i2c_host_kw *host = dev_id;
 	unsigned long flags;
 
-	spin_lock_irqsave(&host->lock, flags);
+	raw_spin_lock_irqsave(&host->lock, flags);
 	del_timer(&host->timeout_timer);
 	kw_i2c_handle_interrupt(host, kw_read_reg(reg_isr));
 	if (host->state != state_idle) {
 		host->timeout_timer.expires = jiffies + KW_POLL_TIMEOUT;
 		add_timer(&host->timeout_timer);
 	}
-	spin_unlock_irqrestore(&host->lock, flags);
+	raw_spin_unlock_irqrestore(&host->lock, flags);
 	return IRQ_HANDLED;
 }
 
@@ -362,7 +362,7 @@ static void kw_i2c_timeout(struct timer_list *t)
 	struct pmac_i2c_host_kw *host = from_timer(host, t, timeout_timer);
 	unsigned long flags;
 
-	spin_lock_irqsave(&host->lock, flags);
+	raw_spin_lock_irqsave(&host->lock, flags);
 
 	/*
 	 * If the timer is pending, that means we raced with the
@@ -377,7 +377,7 @@ static void kw_i2c_timeout(struct timer_list *t)
 		add_timer(&host->timeout_timer);
 	}
  skip:
-	spin_unlock_irqrestore(&host->lock, flags);
+	raw_spin_unlock_irqrestore(&host->lock, flags);
 }
 
 static int kw_i2c_open(struct pmac_i2c_bus *bus)
@@ -470,9 +470,9 @@ static int kw_i2c_xfer(struct pmac_i2c_bus *bus, u8 addrdir, int subsize,
 			unsigned long flags;
 
 			u8 isr = kw_i2c_wait_interrupt(host);
-			spin_lock_irqsave(&host->lock, flags);
+			raw_spin_lock_irqsave(&host->lock, flags);
 			kw_i2c_handle_interrupt(host, isr);
-			spin_unlock_irqrestore(&host->lock, flags);
+			raw_spin_unlock_irqrestore(&host->lock, flags);
 		}
 	}
 
@@ -508,7 +508,7 @@ static struct pmac_i2c_host_kw *__init kw_i2c_host_init(struct device_node *np)
 	}
 	mutex_init(&host->mutex);
 	init_completion(&host->complete);
-	spin_lock_init(&host->lock);
+	raw_spin_lock_init(&host->lock);
 	timer_setup(&host->timeout_timer, kw_i2c_timeout, 0);
 
 	psteps = of_get_property(np, "AAPL,address-step", NULL);
-- 
2.20.1