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Mon, 2 Dec 2019 08:38:27 +0000 From: Yoshihiro Shimoda To: Wolfram Sang CC: "linux-renesas-soc@vger.kernel.org" Subject: RE: [PATCH RFC 4/4] mmc: host: renesas_sdhi_sys_dmac: Set dma_buswidth value to 32 byte Thread-Topic: [PATCH RFC 4/4] mmc: host: renesas_sdhi_sys_dmac: Set dma_buswidth value to 32 byte Thread-Index: AQHVoPwELQfgE6mlPkao0v5O9MIm7aehHbYAgAVtM1A= Date: Mon, 2 Dec 2019 08:38:27 +0000 Message-ID: References: <1574403231-18512-1-git-send-email-yoshihiro.shimoda.uh@renesas.com> <1574403231-18512-5-git-send-email-yoshihiro.shimoda.uh@renesas.com> <20191128210728.GA864@kunai> In-Reply-To: <20191128210728.GA864@kunai> Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=yoshihiro.shimoda.uh@renesas.com; x-originating-ip: [150.249.235.54] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 73cfc0b5-e27a-4da9-d673-08d7770300e5 x-ms-traffictypediagnostic: TYAPR01MB3277: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: renesas.com X-MS-Exchange-CrossTenant-Network-Message-Id: 73cfc0b5-e27a-4da9-d673-08d7770300e5 X-MS-Exchange-CrossTenant-originalarrivaltime: 02 Dec 2019 08:38:27.8535 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 53d82571-da19-47e4-9cb4-625a166a4a2a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: fYMhdkOXec+zyFR2NXytb+zICwmtV2Hqlg3LrEESOk2sOXBU3eNF+N1GNz/EchJOqkETdmRE2aXTlLZZb6Db5KITcbn97LtsdKdETtaPBb3h1s8qb1aiC35/EKG5PxH2 X-MS-Exchange-Transport-CrossTenantHeadersStamped: TYAPR01MB3277 Sender: linux-renesas-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org Hi Wolfram-san, Thank you for your comments! > From: Wolfram Sang, Sent: Friday, November 29, 2019 6:07 AM >=20 > Hi Shimoda-san, >=20 > Interesting series! >=20 > > - .dma_buswidth =3D DMA_SLAVE_BUSWIDTH_4_BYTES, > > + .dma_buswidth =3D DMA_SLAVE_BUSWIDTH_32_BYTES, >=20 > Two very high level questions: >=20 > 1) can't we set dma_priv->dma_buswidth at runtime when we know what the > card is capable of? Either DMA_SLAVE_BUSWIDTH_32_BYTES or > DMA_SLAVE_BUSWIDTH_4_BYTES? Then we don't need to fallback to PIO. > AFAIS, we only Gen2 sets .dma_buswidth in of_data, so we could even > remove it from of_data entirely? As I replied to Ulrich-san on other email thread, for now, rcar-dmac has a = limitation on dmaengine_slave_config(), we should not call it at runtime. But, I don't= think any sd card have such a limitation. In other words, if rcar-dmac doesn't ha= ve the limitation, I think we can change the buswidth at runtime and then we c= an remove the .dma_buswidth from of_data. > 2) Just by grepping in mmc/hosts, I see that no driver uses > DMA_SLAVE_BUSWIDTH_32_BYTES. Do you have an idea why? Because it is the > convenient setting which works for all cards? I also grepped in drivers/dma, and all dmaengine drivers except Renesas rel= ated SoCs don't support DMA_SLAVE_BUSWIDTH_32_BYTES. So, I think no driver uses the 32 bytes on mmc/hosts :) Best regards, Yoshihiro Shimoda > Thanks and kind regards, >=20 > Wolfram