linux-kernel - Re: [PATCH 7/9] drm/i915: Use memcpy_from_page() in gt/uc/intel_uc

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Message-ID: <Y2QQaYBD1ECJDoNP@iweiny-desk3>
Date:   Thu, 3 Nov 2022 12:03:05 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Zhao Liu <zhao1.liu@...ux.intel.com>
CC:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthew Auld <matthew.auld@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Nirmoy Das <nirmoy.das@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Christian König <christian.koenig@....com>,
        <intel-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>,
        Zhenyu Wang <zhenyu.z.wang@...el.com>,
        Zhao Liu <zhao1.liu@...el.com>
Subject: Re: [PATCH 7/9] drm/i915: Use memcpy_from_page() in
 gt/uc/intel_uc_fw.c

On Mon, Oct 17, 2022 at 05:37:23PM +0800, Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@...el.com>
> 
> The use of kmap_atomic() is being deprecated in favor of
> kmap_local_page()[1].
> 
> The main difference between atomic and local mappings is that local
> mappings doesn't disable page faults or preemption.
> 
> In drm/i915/gt/uc/intel_us_fw.c, the function intel_uc_fw_copy_rsa()
> just use the mapping to do memory copy so it doesn't need to disable
> pagefaults and preemption for mapping. Thus the local mapping without
> atomic context (not disable pagefaults / preemption) is enough.
> 
> Therefore, intel_uc_fw_copy_rsa() is a function where the use of
> memcpy_from_page() with kmap_local_page() in place of memcpy() with
> kmap_atomic() is correctly suited.
> 
> Convert the calls of memcpy() with kmap_atomic() / kunmap_atomic() to
> memcpy_from_page() which uses local mapping to copy.
> 
> [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/T/#u
> 
> Suggested-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> Signed-off-by: Zhao Liu <zhao1.liu@...el.com>
> ---
> Suggested by credits:
>   Ira: Referred to his task document and suggestions about using
>        memcpy_from_page() directly.
>   Fabio: Referred to his boiler plate commit message.
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> index b91ad4aede1f..64d56f175d32 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> @@ -962,16 +962,13 @@ size_t intel_uc_fw_copy_rsa(struct intel_uc_fw *uc_fw, void *dst, u32 max_len)
>  
>  		for_each_sgt_page(page, iter, uc_fw->obj->mm.pages) {
>  			u32 len = min_t(u32, size, PAGE_SIZE - offset);
> -			void *vaddr;
>  
>  			if (idx > 0) {
>  				idx--;
>  				continue;
>  			}
>  
> -			vaddr = kmap_atomic(page);
> -			memcpy(dst, vaddr + offset, len);
> -			kunmap_atomic(vaddr);
> +			memcpy_from_page(dst, page, offset, len);
>  
>  			offset = 0;
>  			dst += len;
> -- 
> 2.34.1
>