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[2620:137:e000::1:20]) by mx.google.com with ESMTP id nb8-20020a1709071c8800b008cf5d345700si365192ejc.864.2023.03.30.02.15.16; Thu, 30 Mar 2023 02:15:46 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230052AbjC3JBW (ORCPT + 99 others); Thu, 30 Mar 2023 05:01:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35078 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229613AbjC3JBV (ORCPT ); Thu, 30 Mar 2023 05:01:21 -0400 Received: from 189.cn (ptr.189.cn [183.61.185.101]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 8A5B46EAD for ; Thu, 30 Mar 2023 02:01:19 -0700 (PDT) HMM_SOURCE_IP: 10.64.8.43:38472.1681716573 HMM_ATTACHE_NUM: 0000 HMM_SOURCE_TYPE: SMTP Received: from clientip-114.242.206.180 (unknown [10.64.8.43]) by 189.cn (HERMES) with SMTP id B4C161002CF; Thu, 30 Mar 2023 17:01:17 +0800 (CST) Received: from ([114.242.206.180]) by gateway-151646-dep-7b48884fd-tj646 with ESMTP id f5b9e183632f48f099a5785df2746d73 for tzimmermann@suse.de; Thu, 30 Mar 2023 17:01:18 CST X-Transaction-ID: f5b9e183632f48f099a5785df2746d73 X-Real-From: 15330273260@189.cn X-Receive-IP: 114.242.206.180 X-MEDUSA-Status: 0 Sender: 15330273260@189.cn Message-ID: <740bb1d9-fca2-9171-b548-0422c9e94112@189.cn> Date: Thu, 30 Mar 2023 17:01:17 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH] drm/fbdev-generic: optimize out a redundant assignment clause Content-Language: en-US To: Thomas Zimmermann , Lucas De Marchi Cc: suijingfeng , David Airlie , liyi , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20230325074636.136833-1-15330273260@189.cn> <20230330041726.w7boceq7ljymvfq2@ldmartin-desk2> From: Sui Jingfeng <15330273260@189.cn> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=0.6 required=5.0 tests=FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM,FROM_LOCAL_DIGITS,FROM_LOCAL_HEX,NICE_REPLY_A, SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/3/30 14:57, Thomas Zimmermann wrote: > Hi > > Am 30.03.23 um 06:17 schrieb Lucas De Marchi: >> On Wed, Mar 29, 2023 at 11:04:17AM +0200, Thomas Zimmermann wrote: >>> (cc'ing Lucas) >>> >>> Hi >>> >>> Am 25.03.23 um 08:46 schrieb Sui Jingfeng: >>>>  The assignment already done in drm_client_buffer_vmap(), >>>>  just trival clean, no functional change. >>>> >>>> Signed-off-by: Sui Jingfeng <15330273260@189.cn> >>>> --- >>>>  drivers/gpu/drm/drm_fbdev_generic.c | 5 ++--- >>>>  1 file changed, 2 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_fbdev_generic.c >>>> b/drivers/gpu/drm/drm_fbdev_generic.c >>>> index 4d6325e91565..1da48e71c7f1 100644 >>>> --- a/drivers/gpu/drm/drm_fbdev_generic.c >>>> +++ b/drivers/gpu/drm/drm_fbdev_generic.c >>>> @@ -282,7 +282,7 @@ static int drm_fbdev_damage_blit(struct >>>> drm_fb_helper *fb_helper, >>>>                   struct drm_clip_rect *clip) >>>>  { >>>>      struct drm_client_buffer *buffer = fb_helper->buffer; >>>> -    struct iosys_map map, dst; >>>> +    struct iosys_map map; >>>>      int ret; >>>>      /* >>>> @@ -302,8 +302,7 @@ static int drm_fbdev_damage_blit(struct >>>> drm_fb_helper *fb_helper, >>>>      if (ret) >>>>          goto out; >>>> -    dst = map; >>>> -    drm_fbdev_damage_blit_real(fb_helper, clip, &dst); >>>> +    drm_fbdev_damage_blit_real(fb_helper, clip, &map); >>> >>> I see what you're doing and it's probably correct in this case. >>> >>> But there's a larger issue with this iosys interfaces. Sometimes the >>> address has to be modified (see calls of iosys_map_incr()). That can >>> prevent incorrect uses of the mapping in other places, especially in >>> unmap code. >> >> using a initializer for the cases it's needed IMO would make these kind >> of problems go away, because then the intent is explicit >> >>> >>> I think it would make sense to consider a separate structure for the >>> I/O location. The buffer as a whole would still be represented by >>> struct iosys_map.  And that new structure, let's call it struct >>> iosys_ptr, would point to an actual location within the buffer's >> >> sounds fine to me, but I'd have to take a deeper look later (or when >> someone writes the patch).  It seems we'd replicate almost the entire >> API to just accomodate the 2 structs.  And the different types will lead >> to confusion when one or the other should be used > > I think we can split the current interface onto two categories: > mapping and I/O. The former would use iosys_map and the latter would > use iosys_ptr. And we'd need a helper that turns gets a ptr for a > given map. > > If I find the tine, I'll probably type up a patch. > Then merge this trivial patch first? It will not prohibit anyone achieve a big goal or releasing a better patch in the future. > Best regards > Thomas > >> >> thanks >> Lucas De Marchi >> >>> memory range. A few locations and helpers would need changes, but >>> there are not so many callers that it's an issue.  This would also >>> allow for a few debugging tests that ensure that iosys_ptr always >>> operates within the bounds of an iosys_map. >>> >>> I've long considered this idea, but there was no pressure to work on >>> it. Maybe now. >>> >>> Best regards >>> Thomas >>> >>>>      drm_client_buffer_vunmap(buffer); >>> >>> -- >>> Thomas Zimmermann >>> Graphics Driver Developer >>> SUSE Software Solutions Germany GmbH >>> Maxfeldstr. 5, 90409 Nürnberg, Germany >>> (HRB 36809, AG Nürnberg) >>> Geschäftsführer: Ivo Totev >> >> >> >