Re: [PATCH] drm/fsl-dcu: use flat regmap cache

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Jun 03, 2016 at 03:43:19PM -0700, Stefan Agner wrote:
> Using flat regmap cache instead of RB-tree to avoid the following
> lockdep warning on driver load:
> WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x15c/0x160()
> DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> 
> The RB-tree regmap cache needs to allocate new space on first
> writes. However, allocations in an atomic context (e.g. when a
> spinlock is held) are not allowed. The function regmap_write
> calls map->lock, which acquires a spinlock in the fast_io case.
> Since the FSL DCU driver uses MMIO, the regmap bus of type
> regmap_mmio is being used which has fast_io set to true.
> 
> Use flat regmap cache and specify max register to be large
> enouth to cover all registers available in LS1021a and Vybrids
> register space.
> 
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: stable@vger.kernel.org
> ---
> While regmap cache is used for suspend/resume only (which is
> broken in its current state) Mark noted that using the RB regmap
> cache can also cause issues during initialization of the driver.
> This patch migrates to flat regmap cache (which we can also use
> to fix the issue in stable kernels), and yet another patchset
> moves to the atomic suspend/resume helpers (which will not go
> into stable...)

While talking suspend/resume, I highly recommend
drm_atomic_helper_suspend and drm_atomic_helper_resume. In my experience
dumb safe/restore of registers for restoring modeset state leads to tears.
-Daniel

> 
> Dave, I saw that you just sent out the pull for rc2, will send
> a pull request for rc3 early next week...
> 
> --
> Stefan
> 
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> index 0ec1ad9..dc723f7 100644
> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> @@ -42,9 +42,10 @@ static const struct regmap_config fsl_dcu_regmap_config = {
>  	.reg_bits = 32,
>  	.reg_stride = 4,
>  	.val_bits = 32,
> -	.cache_type = REGCACHE_RBTREE,
> +	.cache_type = REGCACHE_FLAT,
>  
>  	.volatile_reg = fsl_dcu_drm_is_volatile_reg,
> +	.max_register = 0x11fc,
>  };
>  
>  static int fsl_dcu_drm_irq_init(struct drm_device *dev)
> -- 
> 2.8.2
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch