Re: [PATCH v2 6/7] iommu/rockchip: use DMA API to map, to flush cache

[Shunqian Zheng <shunqian.zheng-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi

On 2016年06月10日 17:10, Tomasz Figa wrote:
> Hi,
>
> On Wed, Jun 8, 2016 at 10:26 PM, Shunqian Zheng <zhengsq@rock-chips.com> wrote:
>> Use DMA API instead of architecture internal functions like
>> __cpuc_flush_dcache_area() etc.
>>
>> To support the virtual device like DRM the virtual slave iommu
>> added in the previous patch, attaching to which the DRM can use
>> it own domain->dev for dma_map_*(), dma_sync_*() even VOP is disabled.
>>
>> With this patch, this driver is available for ARM64 like RK3399.
>>
> Could we instead simply allocate coherent memory for page tables using
> dma_alloc_coherent() and skip any flushing on CPU side completely? If
> I'm looking correctly, the driver only reads back the page directory
> when checking if there is a need to allocate new page table, so there
> shouldn't be any significant penalty for disabling the cache.
I try to use dma_alloc_coherent() to replace the dma_map_single(),
but it doesn't work for me properly.
Because the DRM uses the iommu_dma_ops instead the swiotlb_dma_ops after 
attaching
to iommu, so when the iommu domain need to alloc a new page in 
rk_iommu_map(),
it would call:
rk_iommu_map()  --> dma_alloc_coherent()  --> ops->alloc()  --> 
iommu_map() --> rk_iommu_map()

Then I try to reserve memory for coherent so that, dma_alloc_coherent()  
calls dma_alloc_from_coherent()
but not ops->alloc(). But it doesn't work too because when DRM request 
buffer it never uses iommu.
>
> Other than that, please see some comments inline.
>
>> Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
>> ---
>>   drivers/iommu/rockchip-iommu.c | 113 ++++++++++++++++++++++++++---------------
>>   1 file changed, 71 insertions(+), 42 deletions(-)
>>
>> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
>> index d6c3051..aafea6e 100644
>> --- a/drivers/iommu/rockchip-iommu.c
>> +++ b/drivers/iommu/rockchip-iommu.c
>> @@ -4,8 +4,6 @@
>>    * published by the Free Software Foundation.
>>    */
>>
>> -#include <asm/cacheflush.h>
>> -#include <asm/pgtable.h>
>>   #include <linux/compiler.h>
>>   #include <linux/delay.h>
>>   #include <linux/device.h>
>> @@ -61,8 +59,7 @@
>>   #define RK_MMU_IRQ_BUS_ERROR     0x02  /* bus read error */
>>   #define RK_MMU_IRQ_MASK          (RK_MMU_IRQ_PAGE_FAULT | RK_MMU_IRQ_BUS_ERROR)
>>
>> -#define NUM_DT_ENTRIES 1024
>> -#define NUM_PT_ENTRIES 1024
>> +#define NUM_TLB_ENTRIES 1024 /* for both DT and PT */
> Is it necessary to change this in this patch? In general, it's not a
> good idea to mix multiple logical changes together.
Sure, will restore changes in v3.
>
>>   #define SPAGE_ORDER 12
>>   #define SPAGE_SIZE (1 << SPAGE_ORDER)
>> @@ -82,7 +79,9 @@
>>
>>   struct rk_iommu_domain {
>>          struct list_head iommus;
>> +       struct device *dev;
>>          u32 *dt; /* page directory table */
>> +       dma_addr_t dt_dma;
>>          spinlock_t iommus_lock; /* lock for iommus list */
>>          spinlock_t dt_lock; /* lock for modifying page directory table */
>>
>> @@ -98,14 +97,12 @@ struct rk_iommu {
>>          struct iommu_domain *domain; /* domain to which iommu is attached */
>>   };
>>
>> -static inline void rk_table_flush(u32 *va, unsigned int count)
>> +static inline void rk_table_flush(struct device *dev, dma_addr_t dma,
>> +                                 unsigned int count)
>>   {
>> -       phys_addr_t pa_start = virt_to_phys(va);
>> -       phys_addr_t pa_end = virt_to_phys(va + count);
>> -       size_t size = pa_end - pa_start;
>> +       size_t size = count * 4;
> It would be a good idea to specify what "count" is. I'm a bit confused
> that before it meant bytes and now some multiple of 4?
"count" means PT/DT entry count to flush here. I would add some more 
comment on it.

Thank you very much,
Shunqian
>
> Best regards,
> Tomasz
>
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