Re: [PATCH 4/4] drm/i915: Rework workaround data exporting to debugfs

[Damien Lespiau <damien.lespiau@intel.com>]

On Mon, Sep 01, 2014 at 02:28:53PM +0100, Arun Siluvery wrote:
> Now w/a are organized in an array so we know exactly how many of them
> are applied; use the same array while exporting data to debugfs and
> remove the temporary array we currently have in driver priv structure.
> 
> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c     | 41 +++++++++++++++++++++++----------
>  drivers/gpu/drm/i915/i915_drv.h         | 14 -----------
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 15 ++++++++++++
>  drivers/gpu/drm/i915/intel_ringbuffer.h |  8 +++++++
>  4 files changed, 52 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 2727bda..bab0408 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -2465,6 +2465,14 @@ static int i915_wa_registers(struct seq_file *m, void *unused)
>  	struct drm_info_node *node = (struct drm_info_node *) m->private;
>  	struct drm_device *dev = node->minor->dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct intel_ring_context_rodata ro_data;
> +
> +	ret = ring_context_rodata(dev, &ro_data);
> +	if (ret) {
> +		seq_printf(m, "Workarounds applied: 0\n");

seq_puts()

> +		DRM_DEBUG_DRIVER("Workaround table not available !!\n");
> +		return -EINVAL;
> +	}
>  
>  	ret = mutex_lock_interruptible(&dev->struct_mutex);
>  	if (ret)
> @@ -2472,18 +2480,27 @@ static int i915_wa_registers(struct seq_file *m, void *unused)
>  
>  	intel_runtime_pm_get(dev_priv);
>  
> -	seq_printf(m, "Workarounds applied: %d\n", dev_priv->num_wa_regs);
> -	for (i = 0; i < dev_priv->num_wa_regs; ++i) {
> -		u32 addr, mask;
> -
> -		addr = dev_priv->intel_wa_regs[i].addr;
> -		mask = dev_priv->intel_wa_regs[i].mask;
> -		dev_priv->intel_wa_regs[i].value = I915_READ(addr) | mask;
> -		if (dev_priv->intel_wa_regs[i].addr)
> -			seq_printf(m, "0x%X: 0x%08X, mask: 0x%08X\n",
> -				   dev_priv->intel_wa_regs[i].addr,
> -				   dev_priv->intel_wa_regs[i].value,
> -				   dev_priv->intel_wa_regs[i].mask);
> +	seq_printf(m, "Workarounds applied: %d\n", ro_data.num_items/2);
> +	for (i = 0; i < ro_data.num_items; i += 2) {
> +		u32 addr, mask, value;
> +
> +		addr = ro_data.init_context[i];
> +		/*
> +		 * Most of workarounds are  masked registers;
> +		 * to set a bit in lower 16-bits we set a mask bit in
> +		 * upper 16-bits so we can take either of them as mask but
> +		 * it doesn't work if the w/a is about clearing a bit so
> +		 * use upper 16-bits to cover both cases.
> +		 */
> +		mask = ro_data.init_context[i+1] >> 16;

"Most" doesn't seem good here. Either it's "all" and we're happy, or we
need a generic way to describe the W/A (masked register or not). value +
mask is generic enough to code for both cases.

> +
> +		/*
> +		 * value represents the status of other bits in the
> +		 * register besides w/a bits
> +		 */
> +		value  = I915_READ(addr) | mask;
> +		seq_printf(m, "0x%X: 0x%08X, mask: 0x%08X\n",
> +			   addr, value, mask);
>  	}

I still don't get it. 'value' is supposed to be the reference value for
the W/A, but you're or'ing the mask here, so you treat the mask as if it
were the reference value. This won't work if the W/A is about setting
multi-bits fields or about clearing a bit.

The comment is still not clear enough. You're saying "other bits besides
the w/a bits", but or'ing the mask doesn't do that.

Why do we care about the "other bits" in the reference value? they don't
matter. Why use something else than (ro_data.init_context[i+1] & 0xffff)
for the value here (as long we're talking about masked registers)?

-- 
Damien