Re: [PATCH v2 1/3] dma-buf: Add struct dma-buf-map for storing struct dma_buf.vaddr_ptr

[Thomas Zimmermann <tzimmermann@suse.de>]

[-- Attachment #1.1: Type: text/plain, Size: 8945 bytes --]

Hi

Am 23.09.20 um 16:27 schrieb Christian König:
> Am 23.09.20 um 14:32 schrieb Thomas Zimmermann:
>> The new type struct dma_buf_map represents a mapping of dma-buf memory
>> into kernel space. It contains a flag, is_iomem, that signals users to
>> access the mapped memory with I/O operations instead of regular loads
>> and stores.
>>
>> It was assumed that DMA buffer memory can be accessed with regular load
>> and store operations. Some architectures, such as sparc64, require the
>> use of I/O operations to access dma-map buffers that are located in I/O
>> memory. Providing struct dma_buf_map allows drivers to implement this.
>> This was specifically a problem when refreshing the graphics framebuffer
>> on such systems. [1]
>>
>> As the first step, struct dma_buf stores an instance of struct
>> dma_buf_map
>> internally. Afterwards, dma-buf's vmap and vunmap interfaces are be
>> converted. Finally, affected drivers can be fixed.
>>
>> [1]
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fdri-devel%2F20200725191012.GA434957%40ravnborg.org%2F&data=02%7C01%7Cchristian.koenig%40amd.com%7C54486b9682654f3950b808d85fbcb1d3%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637364611338153209&sdata=%2BZm7t8OcgkIxnY%2FdZSLhSbKC7t1y4VW5lINFKwCQv3A%3D&reserved=0
>>
> 
> Only two nit picks below, apart from that Reviewed-by: Christian König
> <christian.koenig@amd.com>
> 
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
>> ---
>>   Documentation/driver-api/dma-buf.rst |  3 +
>>   drivers/dma-buf/dma-buf.c            | 14 ++---
>>   include/linux/dma-buf-map.h          | 87 ++++++++++++++++++++++++++++
>>   include/linux/dma-buf.h              |  3 +-
>>   4 files changed, 99 insertions(+), 8 deletions(-)
>>   create mode 100644 include/linux/dma-buf-map.h
>>
>> diff --git a/Documentation/driver-api/dma-buf.rst
>> b/Documentation/driver-api/dma-buf.rst
>> index 13ea0cc0a3fa..3244c600a9a1 100644
>> --- a/Documentation/driver-api/dma-buf.rst
>> +++ b/Documentation/driver-api/dma-buf.rst
>> @@ -115,6 +115,9 @@ Kernel Functions and Structures Reference
>>   .. kernel-doc:: include/linux/dma-buf.h
>>      :internal:
>>   +.. kernel-doc:: include/linux/dma-buf-map.h
>> +   :internal:
>> +
>>   Reservation Objects
>>   -------------------
>>   diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>> index 58564d82a3a2..5e849ca241a0 100644
>> --- a/drivers/dma-buf/dma-buf.c
>> +++ b/drivers/dma-buf/dma-buf.c
>> @@ -1207,12 +1207,12 @@ void *dma_buf_vmap(struct dma_buf *dmabuf)
>>       mutex_lock(&dmabuf->lock);
>>       if (dmabuf->vmapping_counter) {
>>           dmabuf->vmapping_counter++;
>> -        BUG_ON(!dmabuf->vmap_ptr);
>> -        ptr = dmabuf->vmap_ptr;
>> +        BUG_ON(dma_buf_map_is_null(&dmabuf->vmap_ptr));
>> +        ptr = dmabuf->vmap_ptr.vaddr;
>>           goto out_unlock;
>>       }
>>   -    BUG_ON(dmabuf->vmap_ptr);
>> +    BUG_ON(dma_buf_map_is_set(&dmabuf->vmap_ptr));
>>         ptr = dmabuf->ops->vmap(dmabuf);
>>       if (WARN_ON_ONCE(IS_ERR(ptr)))
>> @@ -1220,7 +1220,7 @@ void *dma_buf_vmap(struct dma_buf *dmabuf)
>>       if (!ptr)
>>           goto out_unlock;
>>   -    dmabuf->vmap_ptr = ptr;
>> +    dmabuf->vmap_ptr.vaddr = ptr;
>>       dmabuf->vmapping_counter = 1;
>>     out_unlock:
>> @@ -1239,15 +1239,15 @@ void dma_buf_vunmap(struct dma_buf *dmabuf,
>> void *vaddr)
>>       if (WARN_ON(!dmabuf))
>>           return;
>>   -    BUG_ON(!dmabuf->vmap_ptr);
>> +    BUG_ON(dma_buf_map_is_null(&dmabuf->vmap_ptr));
>>       BUG_ON(dmabuf->vmapping_counter == 0);
>> -    BUG_ON(dmabuf->vmap_ptr != vaddr);
>> +    BUG_ON(!dma_buf_map_is_vaddr(&dmabuf->vmap_ptr, vaddr));
>>         mutex_lock(&dmabuf->lock);
>>       if (--dmabuf->vmapping_counter == 0) {
>>           if (dmabuf->ops->vunmap)
>>               dmabuf->ops->vunmap(dmabuf, vaddr);
>> -        dmabuf->vmap_ptr = NULL;
>> +        dma_buf_map_clear(&dmabuf->vmap_ptr);
>>       }
>>       mutex_unlock(&dmabuf->lock);
>>   }
>> diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h
>> new file mode 100644
>> index 000000000000..d4b1bb3cc4b0
>> --- /dev/null
>> +++ b/include/linux/dma-buf-map.h
>> @@ -0,0 +1,87 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Pointer to dma-buf-mapped memory, plus helpers.
>> + */
>> +
>> +#ifndef __DMA_BUF_MAP_H__
>> +#define __DMA_BUF_MAP_H__
>> +
>> +#include <linux/io.h>
>> +
>> +/**
>> + * struct dma_buf_map - Pointer to vmap'ed dma-buf memory.
>> + * @vaddr_iomem:    The buffer's address if in I/O memory
>> + * @vaddr:        The buffer's address if in system memory
>> + * @is_iomem:        True if the dma-buf memory is located in I/O
>> + *            memory, or false otherwise.
>> + *
>> + * Calling dma-buf's vmap operation returns a pointer to the buffer.
>> + * Depending on the location of the buffer, users may have to access it
>> + * with I/O operations or memory load/store operations. struct
>> dma_buf_map
>> + * stores the buffer address and a flag that signals the required
>> access.
>> + */
>> +struct dma_buf_map {
>> +    union {
>> +        void __iomem *vaddr_iomem;
>> +        void *vaddr;
>> +    };
>> +    bool is_iomem;
>> +};
>> +
>> +/* API transition helper */
>> +static inline bool dma_buf_map_is_vaddr(const struct dma_buf_map
>> *map, const void *vaddr)
>> +{
>> +    return !map->is_iomem && (map->vaddr == vaddr);
>> +}
>> +
>> +/**
>> + * dma_buf_map_is_null - Tests for a dma-buf mapping to be NULL
>> + * @map:    The dma-buf mapping structure
>> + *
>> + * Depending on the state of struct dma_buf_map.is_iomem, tests if the
>> + * mapping is NULL.
>> + *
>> + * Returns:
>> + * True if the mapping is NULL, or false otherwise.
>> + */
>> +static inline bool dma_buf_map_is_null(const struct dma_buf_map *map)
>> +{
>> +    if (map->is_iomem)
>> +        return map->vaddr_iomem == NULL;
>> +    return map->vaddr == NULL;
> 
> This looks like overkill since both pointers are part of the same union.
> 
> I suggest to test only one and add a comment.

I've been trying to separate I/O and system memory as much as possible.
I'd rather leave it as it is.

Best regards
Thomas

> 
>> +}
>> +
>> +/**
>> + * dma_buf_map_is_set - Tests is the dma-buf mapping has been set
>> + * @map:    The dma-buf mapping structure
>> + *
>> + * Depending on the state of struct dma_buf_map.is_iomem, tests if the
>> + * mapping has been set.
>> + *
>> + * Returns:
>> + * True if the mapping is been set, or false otherwise.
>> + */
>> +static inline bool dma_buf_map_is_set(const struct dma_buf_map *map)
>> +{
>> +    return !dma_buf_map_is_null(map);
>> +}
>> +
>> +/**
>> + * dma_buf_map_clear - Clears a dma-buf mapping structure
>> + * @map:    The dma-buf mapping structure
>> + *
>> + * Clears all fields to zero; including struct dma_buf_map.is_iomem. So
>> + * mapping structures that were set to point to I/O memory are reset for
>> + * system memory. Pointers are cleared to NULL. This is the default.
>> + */
>> +static inline void dma_buf_map_clear(struct dma_buf_map *map)
>> +{
>> +    if (map->is_iomem) {
>> +        map->vaddr_iomem = NULL;
>> +        map->is_iomem = false;
>> +    } else {
>> +        map->vaddr = NULL;
>> +    }
> 
> Maybe just use memset() on the structure.
> 
> Christian.
> 
>> +}
>> +
>> +#endif /* __DMA_BUF_MAP_H__ */
>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
>> index 957b398d30e5..fcc2ddfb6d18 100644
>> --- a/include/linux/dma-buf.h
>> +++ b/include/linux/dma-buf.h
>> @@ -13,6 +13,7 @@
>>   #ifndef __DMA_BUF_H__
>>   #define __DMA_BUF_H__
>>   +#include <linux/dma-buf-map.h>
>>   #include <linux/file.h>
>>   #include <linux/err.h>
>>   #include <linux/scatterlist.h>
>> @@ -309,7 +310,7 @@ struct dma_buf {
>>       const struct dma_buf_ops *ops;
>>       struct mutex lock;
>>       unsigned vmapping_counter;
>> -    void *vmap_ptr;
>> +    struct dma_buf_map vmap_ptr;
>>       const char *exp_name;
>>       const char *name;
>>       spinlock_t name_lock;
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 516 bytes --]