From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 26B4C13AA2E; Sat, 18 Jan 2025 08:37:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737189447; cv=none; b=QN3GyxIjZXHye7uent1d9sLVjCihzj21ZsDmA8kSUvt1SUyHbEqIarRJiF2Vmy9ryYQGXstQfqMW5zTooqU6Ek9+ROKc7p3E1IxMbHFG1k9jRiQeUqJK3jaHgKnwPmDJAX/urtYYcrSR7DLBZb1ZJnvvKHTpuOUt+T9MSXftD0o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737189447; c=relaxed/simple; bh=tvFTbNI16dWEiQ0a1DxdbCn/gVCZieFS78UcbDryCxo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=E2Uu4BMrekSXIly5LdojhKJYoTQvJA3DwRpt6qGMbr1oUibFSSGV3witIOv8C0O3tzOeGdVvMTBk/BXSL+1gXryfaXxrboQjy4flSLc5QBZBKSAwSeh1IB9kzPpAspXLI+jIlIMnlzQToYqTmclfTT9seEHFm9XGhDLUDOkz5uU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Vt5NL/gK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Vt5NL/gK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E47F9C4CED1; Sat, 18 Jan 2025 08:37:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737189446; bh=tvFTbNI16dWEiQ0a1DxdbCn/gVCZieFS78UcbDryCxo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Vt5NL/gKLDm/Wrkb8SUMOQwwRjr3aRNsqTWpIaF7cbZFBb+1wBA2Wg0AIVfoKm9Yc 0rKfOW0O3zSXXRm0tNacj4hNeS26RZs6mtzWuqRs6O0all5P+x6RuvTP0SjFkgpN94 HKFr21WH7OBJaH87vQ4BVs6yE9SHgbd9cnFKygRWCtOO9a5mVIf0EI83Geh4NNWuzx tDKNXIw3SQG3UMPWDv9zWTSh2AeLIT7yVBLrlaOVqtRwXD+8m0480YI49CEl2k1SKN u+yA07OjzyiIyG+4kLTM84IDJsviaBsh3fJN6o5pNljCFhmQ5ymSeeMDD/ROcGwVLd G+MMTBLmFywvg== Message-ID: Date: Sat, 18 Jan 2025 09:37:17 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/12] dt-bindings: display: mediatek: add EXDMA yaml for MT8196 To: =?UTF-8?B?UGF1bC1wbCBDaGVuICjpmbPmn4/pnJYp?= , "robh@kernel.org" , "krzk+dt@kernel.org" , "conor+dt@kernel.org" , "chunkuang.hu@kernel.org" , AngeloGioacchino Del Regno Cc: =?UTF-8?B?U3VubnkgU2hlbiAo5rKI5aeN5aeNKQ==?= , =?UTF-8?B?U2lyaXVzIFdhbmcgKOeOi+eak+aYsSk=?= , =?UTF-8?B?TmFuY3kgTGluICjmnpfmrKPonqIp?= , =?UTF-8?B?WGlhbmRvbmcgV2FuZyAo546L5YWI5YasKQ==?= , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Project_Global_Chrome_Upstream_Group , "linux-mediatek@lists.infradead.org" , =?UTF-8?B?SmFzb24tSkggTGluICjmnpfnnb/npaUp?= , "devicetree@vger.kernel.org" , "fshao@chromium.org" , "p.zabel@pengutronix.de" , =?UTF-8?B?U2luZ28gQ2hhbmcgKOW8teiIiOWciyk=?= , "linux-arm-kernel@lists.infradead.org" , "matthias.bgg@gmail.com" , "treapking@chromium.org" References: <20250110123835.2719824-1-paul-pl.chen@mediatek.com> <20250110123835.2719824-4-paul-pl.chen@mediatek.com> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 17/01/2025 11:36, Paul-pl Chen (陳柏霖) wrote: >>> b/Documentation/devicetree/bindings/display/mediatek/mediatek,exdma >>> .yaml >> >> Filename matching compatible. >> >> Why is this in display? DMA goes to dma. > > Hi Krzysztof , > > Regarding the issue of the EXDMA driver, we have conducted an internal > survey of drivers under the DMA subsystem. We found that EXDMA operates I did not talk about driver. I talked about this patch. Look at patch title - it starts with dt-bindings. Is here anything about driver? No. Why do we talk about driver? > differently from typical DMA drivers, and therefore we believe that the > EXDMA driver may not be suitable to be placed under the > driver/mediatek/drm directory. The main reasons are as follows: > > (1)No Memory Allocation within EXDMA Engine: > The EXDMA engine does not perform memory allocation operations itself. > Instead, it relies on GEM (Graphics Execution Manager) to allocate > memory.Traditional DMA drivers often handle their own memory > allocations, but in the case of EXDMA, memory management is delegated > to GEM. > > (2)Primary Task of EXDMA: > The main function of EXDMA is to transfer buffers allocated by GEM to > the subsequent display pipeline. > EXDMA serves as a bridge between memory allocated by GEM and the > display components, rather than acting as a general-purpose DMA engine. > Based on the points above, we have decided to place the EXDMA driver > under the DRM display subsystem rather than under the DMA subsystem. I don't care if it uses GEM or kernel allocator or even 3rd party allocator. The question is: what is this device? If it is performing DMA, then it should be placed in "dma" directory. The rdma was placed differently but as you can easily check: it was never acked/reviewed, so don't use it as an example. Of course if it does not perform DMA, then it should not be in dma, but then I don't agree on using dma-cells here and anything like that in the driver. Best regards, Krzysztof