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Tue, 3 Sep 2024 01:00:51 +0000 Received: from MW5PR11MB5764.namprd11.prod.outlook.com ([fe80::3c2c:a17f:2516:4dc8]) by MW5PR11MB5764.namprd11.prod.outlook.com ([fe80::3c2c:a17f:2516:4dc8%6]) with mapi id 15.20.7918.024; Tue, 3 Sep 2024 01:00:51 +0000 Message-ID: <33eace43-477e-4d06-86e5-3574019cdaba@windriver.com> Date: Tue, 3 Sep 2024 12:00:42 +1100 User-Agent: Mozilla Thunderbird Subject: Re: [v2] drm/etnaviv: Clear the __GFP_HIGHMEM bit in GFP_HIGHUSER with 32 address To: Sui Jingfeng , "l.stach@pengutronix.de" , "linux+etnaviv@armlinux.org.uk" , "christian.gmeiner@gmail.com" , "airlied@gmail.com" , "daniel@ffwll.ch" Cc: "etnaviv@lists.freedesktop.org" , "dri-devel@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" References: Content-Language: en-US From: wang xiaolei In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: TYCP286CA0113.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:29c::10) To MW5PR11MB5764.namprd11.prod.outlook.com (2603:10b6:303:197::8) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW5PR11MB5764:EE_|MN0PR11MB6157:EE_ X-MS-Office365-Filtering-Correlation-Id: fcd58576-20c8-41df-3f9c-08dccbb3dae0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; 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I have more to say. > > On 2024/8/16 09:55, Wang, Xiaolei wrote: >> Ping ... > > 32 address -> 32-bit address, > > Perhaps, we could improve the commit title a little bit > by writing a more accurate sentence if possible, say: > > drm/etnaviv: Properly request pages from DMA32 zone when needed > > or > > drm/etnaviv: Request pages from DMA32 zone on addressing_limited > > >> thanks >> xiaolei > > Vivante GPU is a 32-bit GPU, it do can access 40-bit physical address > via its MMU(IOMMU). > But this is only possible *after* the MMU has been setup(initialized). > Before GPU page > table is setup(and flush-ed into the GPU's TLB), the device can only > access 32-bit > physical addresses and the addresses has to be physical continues in > ranges. > > The GPU page tables (GART) and command buffer has to reside in low 4GB > address. > >> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c >> b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c >> index 7c7f97793ddd..0e6bdf2d028b 100644 >> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c >> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c >> @@ -844,8 +844,10 @@ int etnaviv_gpu_init(struct etnaviv_gpu *gpu) >>            * request pages for our SHM backend buffers from the DMA32 >> zone to >>            * hopefully avoid performance killing SWIOTLB bounce >> buffering. >>            */ >> -       if (dma_addressing_limited(gpu->dev)) >> +       if (dma_addressing_limited(gpu->dev)) { >>                   priv->shm_gfp_mask |= GFP_DMA32; >> +               priv->shm_gfp_mask &= ~__GFP_HIGHMEM; >> +       } > > The code here  still looks itchy and risky, > because for a i.MX8 SoC with multiple vivante GPU core. > We will modify priv->shm_gfp_mask *multiple* time. > > For the 2D core and the 3D core have different DMA addressing constraint. > Then, only the last(latest) modify will be effective. This lead to the > probe order dependent. > > However this may not be a problem in practice, as usually, all vivante > GPUs in the system will share the same DMA constraints. And the driver > assume that. > > But then, we probably still should not modify the global shared GFP > mask multiple time. > > Now that we do assume that all vivante GPUs in the system share the > same DMA constraints. And the DMA constraints information has been > assigned to the virtual master. The right time to modify the > `priv->shm_gfp_mask` should be in the etnaviv_bind() function. as > this can eliminate overlap(repeat) stores. > > > Please consider move the entire if() {} to etnaviv_bind(), just below > where the 'priv->shm_gfp_mask' was initially initialized. > > or alternatively we can just hard-code to use low 4GM memmory only: > > priv->shm_gfp_mask = GFP_USER | GFP_DMA32 | __GFP_RETRY_MAYFAIL | > __GFP_NOWARN; Thank you very much for your review and suggestion. I will move the entire if() {} to etnaviv_bind() thanks xiaolei > > > Best regards, > Sui > >>           /* Create buffer: */ >>           ret = etnaviv_cmdbuf_init(priv->cmdbuf_suballoc, &gpu->buffer,