Re: [PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock

From: Jonathan Cameron
Date: Sun Feb 14 2021 - 13:20:55 EST

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In reply to: William Breathitt Gray: "[PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock"
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On Fri, 12 Feb 2021 21:13:45 +0900
William Breathitt Gray <vilhelm.gray@xxxxxxxxx> wrote:

> This patch replaces the mutex I/O lock with a spinlock. This is in
> preparation for a subsequent patch adding IRQ support for 104-QUAD-8
> devices; we can't sleep in an interrupt context, so we'll need to use a
> spinlock instead.
>
> Cc: Syed Nayyar Waris <syednwaris@xxxxxxxxx>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@xxxxxxxxx>

Why do these need to be raw_spin_locks?
Normally only need to do that if in code related to interrupt chips etc,
not their use.

Jonathan

> ---
> drivers/counter/104-quad-8.c | 90 +++++++++++++++++++++---------------
> 1 file changed, 53 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> index 41fdbd228be3..2b47f9991acc 100644
> --- a/drivers/counter/104-quad-8.c
> +++ b/drivers/counter/104-quad-8.c
> @@ -16,6 +16,7 @@
> #include <linux/module.h>
> #include <linux/moduleparam.h>
> #include <linux/types.h>
> +#include <linux/spinlock.h>
>
> #define QUAD8_EXTENT 32
>
> @@ -28,6 +29,7 @@ MODULE_PARM_DESC(base, "ACCES 104-QUAD-8 base addresses");
>
> /**
> * struct quad8 - device private data structure
> + * @lock: synchronization lock to prevent I/O race conditions
> * @counter: instance of the counter_device
> * @fck_prescaler: array of filter clock prescaler configurations
> * @preset: array of preset values
> @@ -42,7 +44,7 @@ MODULE_PARM_DESC(base, "ACCES 104-QUAD-8 base addresses");
> * @base: base port address of the device
> */
> struct quad8 {
> - struct mutex lock;
> + raw_spinlock_t lock;
> struct counter_device counter;
> unsigned int fck_prescaler[QUAD8_NUM_COUNTERS];
> unsigned int preset[QUAD8_NUM_COUNTERS];
> @@ -123,6 +125,7 @@ static int quad8_count_read(struct counter_device *counter,
> unsigned int flags;
> unsigned int borrow;
> unsigned int carry;
> + unsigned long irqflags;
> int i;
>
> flags = inb(base_offset + 1);
> @@ -132,7 +135,7 @@ static int quad8_count_read(struct counter_device *counter,
> /* Borrow XOR Carry effectively doubles count range */
> *val = (unsigned long)(borrow ^ carry) << 24;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> /* Reset Byte Pointer; transfer Counter to Output Latch */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_CNTR_OUT,
> @@ -141,7 +144,7 @@ static int quad8_count_read(struct counter_device *counter,
> for (i = 0; i < 3; i++)
> *val |= (unsigned long)inb(base_offset) << (8 * i);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -151,13 +154,14 @@ static int quad8_count_write(struct counter_device *counter,
> {
> struct quad8 *const priv = counter->priv;
> const int base_offset = priv->base + 2 * count->id;
> + unsigned long irqflags;
> int i;
>
> /* Only 24-bit values are supported */
> if (val > 0xFFFFFF)
> return -ERANGE;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> /* Reset Byte Pointer */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP, base_offset + 1);
> @@ -182,7 +186,7 @@ static int quad8_count_write(struct counter_device *counter,
> /* Reset Error flag */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_E, base_offset + 1);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -200,8 +204,9 @@ static int quad8_function_read(struct counter_device *counter,
> {
> struct quad8 *const priv = counter->priv;
> const int id = count->id;
> + unsigned long irqflags;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> if (priv->quadrature_mode[id])
> switch (priv->quadrature_scale[id]) {
> @@ -218,7 +223,7 @@ static int quad8_function_read(struct counter_device *counter,
> else
> *function = COUNTER_FUNCTION_PULSE_DIRECTION;
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -233,10 +238,11 @@ static int quad8_function_write(struct counter_device *counter,
> unsigned int *const scale = priv->quadrature_scale + id;
> unsigned int *const synchronous_mode = priv->synchronous_mode + id;
> const int base_offset = priv->base + 2 * id + 1;
> + unsigned long irqflags;
> unsigned int mode_cfg;
> unsigned int idr_cfg;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> mode_cfg = priv->count_mode[id] << 1;
> idr_cfg = priv->index_polarity[id] << 1;
> @@ -271,7 +277,7 @@ static int quad8_function_write(struct counter_device *counter,
> break;
> default:
> /* should never reach this path */
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
> return -EINVAL;
> }
> }
> @@ -279,7 +285,7 @@ static int quad8_function_write(struct counter_device *counter,
> /* Load mode configuration to Counter Mode Register */
> outb(QUAD8_CTR_CMR | mode_cfg, base_offset);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -407,9 +413,10 @@ static int quad8_index_polarity_set(struct counter_device *counter,
> struct quad8 *const priv = counter->priv;
> const size_t channel_id = signal->id - 16;
> const int base_offset = priv->base + 2 * channel_id + 1;
> + unsigned long irqflags;
> unsigned int idr_cfg = index_polarity << 1;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> idr_cfg |= priv->synchronous_mode[channel_id];
>
> @@ -418,7 +425,7 @@ static int quad8_index_polarity_set(struct counter_device *counter,
> /* Load Index Control configuration to Index Control Register */
> outb(QUAD8_CTR_IDR | idr_cfg, base_offset);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -447,15 +454,16 @@ static int quad8_synchronous_mode_set(struct counter_device *counter,
> struct quad8 *const priv = counter->priv;
> const size_t channel_id = signal->id - 16;
> const int base_offset = priv->base + 2 * channel_id + 1;
> + unsigned long irqflags;
> unsigned int idr_cfg = synchronous_mode;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> idr_cfg |= priv->index_polarity[channel_id] << 1;
>
> /* Index function must be non-synchronous in non-quadrature mode */
> if (synchronous_mode && !priv->quadrature_mode[channel_id]) {
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
> return -EINVAL;
> }
>
> @@ -464,7 +472,7 @@ static int quad8_synchronous_mode_set(struct counter_device *counter,
> /* Load Index Control configuration to Index Control Register */
> outb(QUAD8_CTR_IDR | idr_cfg, base_offset);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -511,6 +519,7 @@ static int quad8_count_mode_write(struct counter_device *counter,
> unsigned int count_mode;
> unsigned int mode_cfg;
> const int base_offset = priv->base + 2 * count->id + 1;
> + unsigned long irqflags;
>
> /* Map Generic Counter count mode to 104-QUAD-8 count mode */
> switch (cnt_mode) {
> @@ -531,7 +540,7 @@ static int quad8_count_mode_write(struct counter_device *counter,
> return -EINVAL;
> }
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> priv->count_mode[count->id] = count_mode;
>
> @@ -545,7 +554,7 @@ static int quad8_count_mode_write(struct counter_device *counter,
> /* Load mode configuration to Counter Mode Register */
> outb(QUAD8_CTR_CMR | mode_cfg, base_offset);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -565,9 +574,10 @@ static int quad8_count_enable_write(struct counter_device *counter,
> {
> struct quad8 *const priv = counter->priv;
> const int base_offset = priv->base + 2 * count->id;
> + unsigned long irqflags;
> unsigned int ior_cfg;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> priv->ab_enable[count->id] = enable;
>
> @@ -576,7 +586,7 @@ static int quad8_count_enable_write(struct counter_device *counter,
> /* Load I/O control configuration */
> outb(QUAD8_CTR_IOR | ior_cfg, base_offset + 1);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -627,16 +637,17 @@ static int quad8_count_preset_write(struct counter_device *counter,
> struct counter_count *count, u64 preset)
> {
> struct quad8 *const priv = counter->priv;
> + unsigned long irqflags;
>
> /* Only 24-bit values are supported */
> if (preset > 0xFFFFFF)
> return -ERANGE;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> quad8_preset_register_set(priv, count->id, preset);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -645,8 +656,9 @@ static int quad8_count_ceiling_read(struct counter_device *counter,
> struct counter_count *count, u64 *ceiling)
> {
> struct quad8 *const priv = counter->priv;
> + unsigned long irqflags;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> /* Range Limit and Modulo-N count modes use preset value as ceiling */
> switch (priv->count_mode[count->id]) {
> @@ -660,7 +672,7 @@ static int quad8_count_ceiling_read(struct counter_device *counter,
> break;
> }
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -669,23 +681,24 @@ static int quad8_count_ceiling_write(struct counter_device *counter,
> struct counter_count *count, u64 ceiling)
> {
> struct quad8 *const priv = counter->priv;
> + unsigned long irqflags;
>
> /* Only 24-bit values are supported */
> if (ceiling > 0xFFFFFF)
> return -ERANGE;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> /* Range Limit and Modulo-N count modes use preset value as ceiling */
> switch (priv->count_mode[count->id]) {
> case 1:
> case 3:
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
> quad8_preset_register_set(priv, count->id, ceiling);
> return 0;
> }
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return -EINVAL;
> }
> @@ -707,12 +720,13 @@ static int quad8_count_preset_enable_write(struct counter_device *counter,
> {
> struct quad8 *const priv = counter->priv;
> const int base_offset = priv->base + 2 * count->id + 1;
> + unsigned long irqflags;
> unsigned int ior_cfg;
>
> /* Preset enable is active low in Input/Output Control register */
> preset_enable = !preset_enable;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> priv->preset_enable[count->id] = preset_enable;
>
> @@ -721,7 +735,7 @@ static int quad8_count_preset_enable_write(struct counter_device *counter,
> /* Load I/O control configuration to Input / Output Control Register */
> outb(QUAD8_CTR_IOR | ior_cfg, base_offset);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -732,22 +746,23 @@ static int quad8_signal_cable_fault_read(struct counter_device *counter,
> {
> struct quad8 *const priv = counter->priv;
> const size_t channel_id = signal->id / 2;
> + unsigned long irqflags;
> bool disabled;
> unsigned int status;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> disabled = !(priv->cable_fault_enable & BIT(channel_id));
>
> if (disabled) {
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
> return -EINVAL;
> }
>
> /* Logic 0 = cable fault */
> status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> /* Mask respective channel and invert logic */
> *cable_fault = !(status & BIT(channel_id));
> @@ -773,9 +788,10 @@ static int quad8_signal_cable_fault_enable_write(struct counter_device *counter,
> {
> struct quad8 *const priv = counter->priv;
> const size_t channel_id = signal->id / 2;
> + unsigned long irqflags;
> unsigned int cable_fault_enable;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> if (enable)
> priv->cable_fault_enable |= BIT(channel_id);
> @@ -787,7 +803,7 @@ static int quad8_signal_cable_fault_enable_write(struct counter_device *counter,
>
> outb(cable_fault_enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -810,8 +826,9 @@ static int quad8_signal_fck_prescaler_write(struct counter_device *counter,
> struct quad8 *const priv = counter->priv;
> const size_t channel_id = signal->id / 2;
> const int base_offset = priv->base + 2 * channel_id;
> + unsigned long irqflags;
>
> - mutex_lock(&priv->lock);
> + raw_spin_lock_irqsave(&priv->lock, irqflags);
>
> priv->fck_prescaler[channel_id] = prescaler;
>
> @@ -823,7 +840,7 @@ static int quad8_signal_fck_prescaler_write(struct counter_device *counter,
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_PRESET_PSC,
> base_offset + 1);
>
> - mutex_unlock(&priv->lock);
> + raw_spin_unlock_irqrestore(&priv->lock, irqflags);
>
> return 0;
> }
> @@ -992,8 +1009,7 @@ static int quad8_probe(struct device *dev, unsigned int id)
> priv->counter.priv = priv;
> priv->base = base[id];
>
> - /* Initialize mutex */
> - mutex_init(&priv->lock);
> + raw_spin_lock_init(&priv->lock);
>
> /* Reset all counters and disable interrupt function */
> outb(QUAD8_CHAN_OP_RESET_COUNTERS, base[id] + QUAD8_REG_CHAN_OP);

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In reply to: William Breathitt Gray: "[PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock"
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