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[209.85.220.65]) by mx.google.com with SMTPS id l190sor3178680vkl.34.2019.07.01.11.07.35 for (Google Transport Security); Mon, 01 Jul 2019 11:07:35 -0700 (PDT) Received-SPF: pass (google.com: domain of pankajssuryawanshi@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=B+mTkh6V; spf=pass (google.com: domain of pankajssuryawanshi@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=pankajssuryawanshi@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lWONYKiUC+xNG+v0x99Ltv7YhSq18V7iywQoniSnrLY=; b=B+mTkh6VPC/HVnQ/2aPY6tcq2AbxaF1Ieqvp+5l4ijk9/nrIuBAJwhSsYqD/Lkik4W x+k4pLd8gMGKtMhht3Fll8Z+BbzMOMLQb/FqBjxPYlLYt2xkivfIRECPwxqWvzkYSwms q78SVjZsa2BdoiPBS9C0KhLfSN7Sh4cMPnid6WAwR0eh962wv/tCSUypcmIQJbluwuBd pqNgcsOw/e/yvw1i7IGN1XsbMx3m2art1A/7FZf8nLPSrCuoPP/PtgwZ2stipavisg9I t2MwBx7coZG+aEcR35I2h4h1t/ZprqqwTewkKoYWgFEBsg6qwTAj0pnUZtGPsqbMR/tb PXqg== X-Google-Smtp-Source: APXvYqwRJwKQv7q3x+bK0rhEHYsq3B5RUxQ/uPaJ6fmEtHv4AFhRjDw9aFEkw+axhgsNwnA0UOwULvb0Zrsqeu6li5Q= X-Received: by 2002:a1f:2896:: with SMTP id o144mr3222112vko.73.1562004455408; Mon, 01 Jul 2019 11:07:35 -0700 (PDT) MIME-Version: 1.0 References: <20190626175131.GA17250@infradead.org> <0725b9aa-0523-daef-b4ff-7e2dd910cf3c@arm.com> In-Reply-To: <0725b9aa-0523-daef-b4ff-7e2dd910cf3c@arm.com> From: Pankaj Suryawanshi Date: Mon, 1 Jul 2019 23:37:24 +0530 Message-ID: Subject: Re: DMA-API attr - DMA_ATTR_NO_KERNEL_MAPPING To: Robin Murphy Cc: Christoph Hellwig , linux-mm@kvack.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Vlastimil Babka , Michal Hocko Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 1, 2019 at 11:24 PM Robin Murphy wrote: > > On 01/07/2019 18:47, Pankaj Suryawanshi wrote: > >> If you want a kernel mapping, *don't* explicitly request not to have a > >> kernel mapping in the first place. It's that simple. > >> > > > > Do you mean do not use dma-api ? because if i used dma-api it will give you > > mapped virtual address. > > or i have to use directly cma_alloc() in my driver. // if i used this > > approach i need to reserved more vmalloc area. > > No, I mean just call dma_alloc_attrs() normally *without* adding the > DMA_ATTR_NO_KERNEL_MAPPING flag. That flag means "I never ever want to > make CPU accesses to this buffer from the kernel" - that is clearly not > the case for your code, so it is utterly nonsensical to still pass the > flag but try to hack around it later. Actually my use case is that i want virtual mapping only when i will play video as my vpu/gpu driver is design like that. and i am using 32-bit so virtual memory is splitted as 3G/1G so dont have enough memory for all the time to mapped with kernel space. Lets say i am allocating 400MB for driver but i want only 30MB for virtual mapping (not everytime) that is the case. > > > Robin.