Subject: [PATCH 1/6] omap: iommu: remove redundant clock usage

From: [email-masked] (Cousson, Benoit)
Date: Sat, 06 Nov 2010 15:11:02 -0400

On 11/5/2010 9:19 PM, Ramirez Luna, Omar wrote:
> iommu driver is meant to provide control of mmu hardware blocks

A dot is missing here, and a capital letter should follow.

> its current users (MMUs) are part of larger subsystems and do not
> have a dedicated clock as the one they use is shared with the
> entire subsystem, it doesn't make sense to enable/disable on each
> register read/write operation as the driver using its interface
> should also be handling the same clock.
>
> iommu should only enable/disable the clock on mmu request/free from
> the driver wanting to use it.

Mmm, I'm not necessarily convinced by that explanation.
If in a next revision, we change the clock partitioning and provide a 
dedicated clock for the mmu, it will not work anymore.
I don't thing you should assume anything about the current partitioning.

That being said, when you will change that code to switch to runtime PM, 
you will end up managing the module state in the ISR context.

Regards,
Benoit

>
> Signed-off-by: Omar Ramirez Luna<[email-masked]>
> ---
>   arch/arm/plat-omap/iommu.c |   38 +++++---------------------------------
>   1 files changed, 5 insertions(+), 33 deletions(-)
>
> diff --git a/arch/arm/plat-omap/iommu.c b/arch/arm/plat-omap/iommu.c
> index 6cd151b..de992c8 100644
> --- a/arch/arm/plat-omap/iommu.c
> +++ b/arch/arm/plat-omap/iommu.c
> @@ -108,7 +108,6 @@ static int iommu_enable(struct iommu *obj)
>
>   	err = arch_iommu->enable(obj);
>
> -	clk_disable(obj->clk);
>   	return err;
>   }
>
> @@ -117,8 +116,6 @@ static void iommu_disable(struct iommu *obj)
>   	if (!obj)
>   		return;
>
> -	clk_enable(obj->clk);
> -
>   	arch_iommu->disable(obj);
>
>   	clk_disable(obj->clk);
> @@ -237,20 +234,16 @@ static struct cr_regs __iotlb_read_cr(struct iommu *obj, int n)
>    **/
>   int load_iotlb_entry(struct iommu *obj, struct iotlb_entry *e)
>   {
> -	int err = 0;
>   	struct iotlb_lock l;
>   	struct cr_regs *cr;
>
>   	if (!obj || !obj->nr_tlb_entries || !e)
>   		return -EINVAL;
>
> -	clk_enable(obj->clk);
> -
>   	iotlb_lock_get(obj,&l);
>   	if (l.base == obj->nr_tlb_entries) {
>   		dev_warn(obj->dev, "%s: preserve entries full\n", __func__);
> -		err = -EBUSY;
> -		goto out;
> +		return -EBUSY;
>   	}
>   	if (!e->prsvd) {
>   		int i;
> @@ -262,8 +255,7 @@ int load_iotlb_entry(struct iommu *obj, struct iotlb_entry *e)
>
>   		if (i == obj->nr_tlb_entries) {
>   			dev_dbg(obj->dev, "%s: full: no entry\n", __func__);
> -			err = -EBUSY;
> -			goto out;
> +			return -EBUSY;
>   		}
>
>   		iotlb_lock_get(obj,&l);
> @@ -273,10 +265,8 @@ int load_iotlb_entry(struct iommu *obj, struct iotlb_entry *e)
>   	}
>
>   	cr = iotlb_alloc_cr(obj, e);
> -	if (IS_ERR(cr)) {
> -		clk_disable(obj->clk);
> +	if (IS_ERR(cr))
>   		return PTR_ERR(cr);
> -	}
>
>   	iotlb_load_cr(obj, cr);
>   	kfree(cr);
> @@ -287,9 +277,8 @@ int load_iotlb_entry(struct iommu *obj, struct iotlb_entry *e)
>   	if (++l.vict == obj->nr_tlb_entries)
>   		l.vict = l.base;
>   	iotlb_lock_set(obj,&l);
> -out:
> -	clk_disable(obj->clk);
> -	return err;
> +
> +	return 0;
>   }
>   EXPORT_SYMBOL_GPL(load_iotlb_entry);
>
> @@ -305,8 +294,6 @@ void flush_iotlb_page(struct iommu *obj, u32 da)
>   	int i;
>   	struct cr_regs cr;
>
> -	clk_enable(obj->clk);
> -
>   	for_each_iotlb_cr(obj, obj->nr_tlb_entries, i, cr) {
>   		u32 start;
>   		size_t bytes;
> @@ -324,7 +311,6 @@ void flush_iotlb_page(struct iommu *obj, u32 da)
>   			iommu_write_reg(obj, 1, MMU_FLUSH_ENTRY);
>   		}
>   	}
> -	clk_disable(obj->clk);
>
>   	if (i == obj->nr_tlb_entries)
>   		dev_dbg(obj->dev, "%s: no page for %08x\n", __func__, da);
> @@ -359,15 +345,11 @@ void flush_iotlb_all(struct iommu *obj)
>   {
>   	struct iotlb_lock l;
>
> -	clk_enable(obj->clk);
> -
>   	l.base = 0;
>   	l.vict = 0;
>   	iotlb_lock_set(obj,&l);
>
>   	iommu_write_reg(obj, 1, MMU_GFLUSH);
> -
> -	clk_disable(obj->clk);
>   }
>   EXPORT_SYMBOL_GPL(flush_iotlb_all);
>
> @@ -382,9 +364,7 @@ EXPORT_SYMBOL_GPL(flush_iotlb_all);
>    */
>   void iommu_set_twl(struct iommu *obj, bool on)
>   {
> -	clk_enable(obj->clk);
>   	arch_iommu->set_twl(obj, on);
> -	clk_disable(obj->clk);
>   }
>   EXPORT_SYMBOL_GPL(iommu_set_twl);
>
> @@ -395,12 +375,8 @@ ssize_t iommu_dump_ctx(struct iommu *obj, char *buf, ssize_t bytes)
>   	if (!obj || !buf)
>   		return -EINVAL;
>
> -	clk_enable(obj->clk);
> -
>   	bytes = arch_iommu->dump_ctx(obj, buf, bytes);
>
> -	clk_disable(obj->clk);
> -
>   	return bytes;
>   }
>   EXPORT_SYMBOL_GPL(iommu_dump_ctx);
> @@ -412,7 +388,6 @@ static int __dump_tlb_entries(struct iommu *obj, struct cr_regs *crs, int num)
>   	struct cr_regs tmp;
>   	struct cr_regs *p = crs;
>
> -	clk_enable(obj->clk);
>   	iotlb_lock_get(obj,&saved);
>
>   	for_each_iotlb_cr(obj, num, i, tmp) {
> @@ -422,7 +397,6 @@ static int __dump_tlb_entries(struct iommu *obj, struct cr_regs *crs, int num)
>   	}
>
>   	iotlb_lock_set(obj,&saved);
> -	clk_disable(obj->clk);
>
>   	return  p - crs;
>   }
> @@ -795,9 +769,7 @@ static irqreturn_t iommu_fault_handler(int irq, void *data)
>   	if (!err)
>   		return IRQ_HANDLED;
>
> -	clk_enable(obj->clk);
>   	stat = iommu_report_fault(obj,&da);
> -	clk_disable(obj->clk);
>   	if (!stat)
>   		return IRQ_HANDLED;
>