iMX6 devices suffer from an errata (ERR005174) where the audio FIFO can be emptied while it is partially full, resulting in misalignment of the audio samples.
To prevent this, the errata workaround recommends writing N as zero until the audio FIFO has been loaded by DMA. Writing N=0 prevents the HDMI bridge from reading from the audio FIFO, effectively disabling audio.
This means we need to provide the audio driver with a pair of functions to enable/disable audio. These are dw_hdmi_audio_enable() and dw_hdmi_audio_disable().
A spinlock is introduced to ensure that setting the CTS/N values can't race, ensuring that the audio driver calling the enable/disable functions (which are called in an atomic context) can't race with a modeset.
Signed-off-by: Russell King rmk+kernel@arm.linux.org.uk --- drivers/gpu/drm/bridge/dw_hdmi.c | 34 +++++++++++++++++++++++++++++++++- include/drm/bridge/dw_hdmi.h | 2 ++ 2 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c index 0369fab5c695..adda3a988f36 100644 --- a/drivers/gpu/drm/bridge/dw_hdmi.c +++ b/drivers/gpu/drm/bridge/dw_hdmi.c @@ -18,6 +18,7 @@ #include <linux/hdmi.h> #include <linux/mutex.h> #include <linux/of_device.h> +#include <linux/spinlock.h>
#include <drm/drm_of.h> #include <drm/drmP.h> @@ -124,8 +125,12 @@ struct dw_hdmi { struct i2c_adapter *ddc; void __iomem *regs;
+ spinlock_t audio_lock; struct mutex audio_mutex; unsigned int sample_rate; + unsigned int audio_cts; + unsigned int audio_n; + bool audio_enable; int ratio;
void (*write)(struct dw_hdmi *hdmi, u8 val, int offset); @@ -347,7 +352,11 @@ static void hdmi_set_clk_regenerator(struct dw_hdmi *hdmi, dev_dbg(hdmi->dev, "%s: samplerate=%ukHz ratio=%d pixelclk=%luMHz N=%d cts=%d\n", __func__, sample_rate, ratio, pixel_clk, n, cts);
- hdmi_set_cts_n(hdmi, cts, n); + spin_lock_irq(&hdmi->audio_lock); + hdmi->audio_n = n; + hdmi->audio_cts = cts; + hdmi_set_cts_n(hdmi, cts, hdmi->audio_enable ? n : 0); + spin_unlock_irq(&hdmi->audio_lock); }
static void hdmi_init_clk_regenerator(struct dw_hdmi *hdmi) @@ -376,6 +385,28 @@ void dw_hdmi_set_sample_rate(struct dw_hdmi *hdmi, unsigned int rate) } EXPORT_SYMBOL_GPL(dw_hdmi_set_sample_rate);
+void dw_hdmi_audio_enable(struct dw_hdmi *hdmi) +{ + unsigned long flags; + + spin_lock_irqsave(&hdmi->audio_lock, flags); + hdmi->audio_enable = true; + hdmi_set_cts_n(hdmi, hdmi->audio_cts, hdmi->audio_n); + spin_unlock_irqrestore(&hdmi->audio_lock, flags); +} +EXPORT_SYMBOL_GPL(dw_hdmi_audio_enable); + +void dw_hdmi_audio_disable(struct dw_hdmi *hdmi) +{ + unsigned long flags; + + spin_lock_irqsave(&hdmi->audio_lock, flags); + hdmi->audio_enable = false; + hdmi_set_cts_n(hdmi, hdmi->audio_cts, 0); + spin_unlock_irqrestore(&hdmi->audio_lock, flags); +} +EXPORT_SYMBOL_GPL(dw_hdmi_audio_disable); + /* * this submodule is responsible for the video data synchronization. * for example, for RGB 4:4:4 input, the data map is defined as @@ -1578,6 +1609,7 @@ int dw_hdmi_bind(struct device *dev, struct device *master, hdmi->encoder = encoder;
mutex_init(&hdmi->audio_mutex); + spin_lock_init(&hdmi->audio_lock);
of_property_read_u32(np, "reg-io-width", &val);
diff --git a/include/drm/bridge/dw_hdmi.h b/include/drm/bridge/dw_hdmi.h index 763af51e1d60..bae79f3c4d28 100644 --- a/include/drm/bridge/dw_hdmi.h +++ b/include/drm/bridge/dw_hdmi.h @@ -63,5 +63,7 @@ int dw_hdmi_bind(struct device *dev, struct device *master, const struct dw_hdmi_plat_data *plat_data);
void dw_hdmi_set_sample_rate(struct dw_hdmi *hdmi, unsigned int rate); +void dw_hdmi_audio_enable(struct dw_hdmi *hdmi); +void dw_hdmi_audio_disable(struct dw_hdmi *hdmi);
#endif /* __IMX_HDMI_H__ */