[PATCH 04/19] drm/i915/gt: Add helper for shmem copy to iosys_map

[Thomas Zimmermann]

Hi

Am 04.02.22 um 18:44 schrieb Lucas De Marchi:
> Add a variant of shmem_read() that takes a iosys_map pointer rather
> than a plain pointer as argument. It's mostly a copy __shmem_rw() but
> adapting the api and removing the write support since there's currently
> only need to use iosys_map as destination.
> 
> Reworking __shmem_rw() to share the implementation was tempting, but
> finding a good balance between reuse and clarity pushed towards a little
> code duplication. Since the function is small, just add the similar
> function with a copy/paste/adapt approach.
> 
> Cc: Matt Roper <matthew.d.roper at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Matthew Auld <matthew.auld at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
> ---
>   drivers/gpu/drm/i915/gt/shmem_utils.c | 33 +++++++++++++++++++++++++++
>   drivers/gpu/drm/i915/gt/shmem_utils.h |  3 +++
>   2 files changed, 36 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.c b/drivers/gpu/drm/i915/gt/shmem_utils.c
> index 0683b27a3890..764adefdb4be 100644
> --- a/drivers/gpu/drm/i915/gt/shmem_utils.c
> +++ b/drivers/gpu/drm/i915/gt/shmem_utils.c
> @@ -3,6 +3,7 @@
>    * Copyright © 2020 Intel Corporation
>    */
>   
> +#include <linux/iosys-map.h>
>   #include <linux/mm.h>
>   #include <linux/pagemap.h>
>   #include <linux/shmem_fs.h>
> @@ -123,6 +124,38 @@ static int __shmem_rw(struct file *file, loff_t off,
>   	return 0;
>   }
>   

Here's a good example of how to avoid iosys_map_incr() and use the 
memcpy offset:

> +int shmem_read_to_iosys_map(struct file *file, loff_t off,
> +			    struct iosys_map *map, size_t len)
> +{
> +	struct iosys_map map_iter = *map;

Rather replace map_iter with something like

   unsigned long map_off = 0;

> +	unsigned long pfn;
> +
> +	for (pfn = off >> PAGE_SHIFT; len; pfn++) {
> +		unsigned int this =
> +			min_t(size_t, PAGE_SIZE - offset_in_page(off), len);
> +		struct page *page;
> +		void *vaddr;
> +
> +		page = shmem_read_mapping_page_gfp(file->f_mapping, pfn,
> +						   GFP_KERNEL);
> +		if (IS_ERR(page))
> +			return PTR_ERR(page);
> +
> +		vaddr = kmap(page);
> +		iosys_map_memcpy_to(&map_iter, 0, vaddr + offset_in_page(off),
> +				    this);

Use map_off to index into map directly.

> +		mark_page_accessed(page);
> +		kunmap(page);
> +		put_page(page);
> +
> +		len -= this;
> +		iosys_map_incr(&map_iter, this);

Raplace iosys_map_incr() with map_off += this;

> +		off = 0;

Maybe off += this ?

I think this pattern should be applied to all similar code. As you 
already noted, iosys_map_incr() is problematic.

Best regards
Thomas

> +	}
> +
> +	return 0;
> +}
> +
>   int shmem_read(struct file *file, loff_t off, void *dst, size_t len)
>   {
>   	return __shmem_rw(file, off, dst, len, false);
> diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.h b/drivers/gpu/drm/i915/gt/shmem_utils.h
> index c1669170c351..e1784999faee 100644
> --- a/drivers/gpu/drm/i915/gt/shmem_utils.h
> +++ b/drivers/gpu/drm/i915/gt/shmem_utils.h
> @@ -8,6 +8,7 @@
>   
>   #include <linux/types.h>
>   
> +struct iosys_map;
>   struct drm_i915_gem_object;
>   struct file;
>   
> @@ -17,6 +18,8 @@ struct file *shmem_create_from_object(struct drm_i915_gem_object *obj);
>   void *shmem_pin_map(struct file *file);
>   void shmem_unpin_map(struct file *file, void *ptr);
>   
> +int shmem_read_to_iosys_map(struct file *file, loff_t off,
> +			    struct iosys_map *map, size_t len);
>   int shmem_read(struct file *file, loff_t off, void *dst, size_t len);
>   int shmem_write(struct file *file, loff_t off, void *src, size_t len);
>   

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