From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Brodkin Subject: Re: [RFC 0/2] dw_mmc: add multislot support Date: Fri, 20 Apr 2018 07:42:13 +0000 Message-ID: <1524210132.4614.4.camel@synopsys.com> References: <20180417121130.25281-1-Eugeniy.Paltsev@synopsys.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: Content-Language: en-US Content-ID: Sender: linux-kernel-owner@vger.kernel.org To: "ulf.hansson@linaro.org" Cc: "jh80.chung@samsung.com" , "linux-kernel@vger.kernel.org" , "linux-mmc@vger.kernel.org" , "krzk@kernel.org" , "Eugeniy.Paltsev@synopsys.com" , "linux-snps-arc@lists.infradead.org" , "kgene@kernel.org" , "shawn.lin@rock-chips.com" , "linux-arm-kernel@lists.infradead.org" , "linux-samsung-soc@vger.kernel.org" List-Id: linux-mmc@vger.kernel.org SGkgVWxmLA0KDQpPbiBGcmksIDIwMTgtMDQtMjAgYXQgMDk6MzUgKzAyMDAsIFVsZiBIYW5zc29u IHdyb3RlOg0KPiBbLi4uXQ0KPiANCj4gPiANCj4gPiAyLiBBZGQgbWlzc2luZyBzdHVmZiB0byBz dXBwb3J0IG11bHRpc2xvdCBtb2RlIGluIERlc2lnbldhcmUgTU1DIGRyaXZlci4NCj4gPiAgKiBB ZGQgbWlzc2luZyBzbG90IHN3aXRjaCB0byBfX2R3X21jaV9zdGFydF9yZXF1ZXN0KCkgZnVuY3Rp b24uDQo+ID4gICogUmVmYWN0b3Igc2V0X2lvcyBmdW5jdGlvbjoNCj4gPiAgICBhKSBDYWxjdWxh dGUgY29tbW9uIGNsb2NrIHdoaWNoIGlzDQo+ID4gICAgICAgc3VpdGFibGUgZm9yIGFsbCBzbG90 cyBpbnN0ZWFkIG9mIGRpcmVjdGx5IHVzZSBjbG9jayB2YWx1ZQ0KPiA+ICAgICAgIHByb3ZpZGVk IGJ5IG1tYyBjb3JlLiBXZSBjYWxjdWxhdGUgY29tbW9uIGNsb2NrIGFzIHRoZSBtaW5pbXVtDQo+ ID4gICAgICAgYW1vbmcgZWFjaCB1c2VkIHNsb3QgY2xvY2tzLiBUaGlzIGNsb2NrIGlzIGNhbGN1 bGF0ZWQgaW4NCj4gPiAgICAgICBkd19tY2lfY2FsY19jb21tb25fY2xvY2soKSBmdW5jdGlvbiB3 aGljaCBpcyBjYWxsZWQNCj4gPiAgICAgICBmcm9tIHNldF9pb3MoKQ0KPiA+ICAgIGIpIERpc2Fi bGUgY2xvY2sgb25seSBpZiBubyBvdGhlciBzbG90cyBhcmUgT04uDQo+ID4gICAgYykgU2V0dXAg Y2xvY2sgZGlyZWN0bHkgaW4gc2V0X2lvcygpIG9ubHkgaWYgbm8gb3RoZXIgc2xvdHMNCj4gPiAg ICAgICBhcmUgT04uIE90aGVyd2lzZSBhZGp1c3QgY2xvY2sgaW4gX19kd19tY2lfc3RhcnRfcmVx dWVzdCgpDQo+ID4gICAgICAgZnVuY3Rpb24gYmVmb3JlIHNsb3Qgc3dpdGNoLg0KPiA+ICAgIGQp IE1vdmUgdGltaW5ncyBhbmQgYnVzX3dpZHRoIHNldHVwIHRvIHNlcGFyYXRlIGZ1bmNpb25zLg0K PiA+ICAqIFVzZSB0aW1pbmcgZmllbGQgaW4gZWFjaCBzbG90IHN0cnVjdHVyZSBpbnN0ZWFkIG9m IGNvbW1vbiBmaWVsZCBpbg0KPiA+ICAgIGhvc3Qgc3RydWN0dXJlLg0KPiA+ICAqIEFkZCBsb2Nr cyB0byBzZXJpYWxpemUgYWNjZXNzIHRvIHJlZ2lzdGVycy4NCj4gDQo+IFNvcnJ5LCBidXQgdGhp cyBpcyBhIGhhY2sgdG8gKnRyeSogdG8gbWFrZSBtdWx0aS1zbG90IHdvcmsgYW5kIHRoaXMNCj4g aXNuJ3Qgc3VmZmljaWVudC4gVGhlcmUgd2VyZSBnb29kIHJlYXNvbnMgdG8gd2h5IHRoZSBlYXJs aWVyDQo+IG5vbi13b3JraW5nIG11bHRpIHNsb3Qgc3VwcG9ydCB3YXMgcmVtb3ZlZCBmcm9tIGR3 X21tYy4NCj4gDQo+IExldCBtZSBlbGFib3JhdGUgYSBiaXQgZm9yIHlvdXIgdW5kZXJzdGFuZGlu Zy4gVGhlIGNvcmUgdXNlcyBhIGhvc3QNCj4gbG9jayAobW1jX2NsYWltfHJlbGVhc2VfaG9zdCgp KSB0byBzZXJpYWxpemUgb3BlcmF0aW9ucyBhbmQgY29tbWFuZHMsDQo+IGFzIHRvIGNvbmZpcm0g dG8gdGhlIFNEL1NESU8vKGUpTU1DIHNwZWNzLiBUaGUgYWJvdmUgY2hhbmdlcyBnaXZlcyBubw0K PiBndWFyYW50ZWVzIGZvciB0aGlzLiBUbyBtYWtlIHRoYXQgd29yaywgd2Ugd291bGQgbmVlZCBh ICJtbWMgYnVzIGxvY2siDQo+IHRvIGJlIG1hbmFnZWQgYnkgdGhlIGNvcmUuDQo+IA0KPiBIb3dl dmVyLCBpbnZlbnRpbmcgYSAibW1jIGJ1cyBsb2NrIiB3b3VsZCBsZWFkIHRvIG90aGVyIHByb2Js ZW1zDQo+IHJlbGF0ZWQgdG8gSS9PIHNjaGVkdWxpbmcgZm9yIHVwcGVyIGxheWVycyAtIGl0IHNp bXBseSBicmVha3MuIEZvcg0KPiBleGFtcGxlLCBJL08gcmVxdWVzdHMgZm9yIG9uZSBjYXJkL3Ns b3QgY2FuIHRoZW4gc3RhcnZlIEkvTyByZXF1ZXN0cw0KPiByZWFjaGluZyBhbm90aGVyIGNhcmQv c2xvdC4NCg0KU28gYXJlIHlvdSBzYXlpbmcgdGhhdCBtdWx0aS1zbG90IHN1cHBvcnQgaXMgYSBu byBnbyBpbiBnZW5lcmFsIG9yIGl0IGlzIG9ubHkNCmFwcGxpY2FibGUgdG8gRFcgTU1DIChJIHJl YWxseSBkb3VidCB0aGF0J3MgYSBjYXNlKT8NCg0KQlRXIHRoZXJlJ3JlIG90aGVyIGNvbnRyb2xs ZXJzIHRoYXQgc2VlbSB0byBzdXBwb3J0IG11bHRpLXNsb3QgbGlrZSBBdG1lbCBldGMuDQoNCi1B bGV4ZXk= From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey.Brodkin@synopsys.com (Alexey Brodkin) Date: Fri, 20 Apr 2018 07:42:13 +0000 Subject: [RFC 0/2] dw_mmc: add multislot support In-Reply-To: References: <20180417121130.25281-1-Eugeniy.Paltsev@synopsys.com> List-ID: Message-ID: <1524210132.4614.4.camel@synopsys.com> To: linux-snps-arc@lists.infradead.org Hi Ulf, On Fri, 2018-04-20@09:35 +0200, Ulf Hansson wrote: > [...] > > > > > 2. Add missing stuff to support multislot mode in DesignWare MMC driver. > > * Add missing slot switch to __dw_mci_start_request() function. > > * Refactor set_ios function: > > a) Calculate common clock which is > > suitable for all slots instead of directly use clock value > > provided by mmc core. We calculate common clock as the minimum > > among each used slot clocks. This clock is calculated in > > dw_mci_calc_common_clock() function which is called > > from set_ios() > > b) Disable clock only if no other slots are ON. > > c) Setup clock directly in set_ios() only if no other slots > > are ON. Otherwise adjust clock in __dw_mci_start_request() > > function before slot switch. > > d) Move timings and bus_width setup to separate funcions. > > * Use timing field in each slot structure instead of common field in > > host structure. > > * Add locks to serialize access to registers. > > Sorry, but this is a hack to *try* to make multi-slot work and this > isn't sufficient. There were good reasons to why the earlier > non-working multi slot support was removed from dw_mmc. > > Let me elaborate a bit for your understanding. The core uses a host > lock (mmc_claim|release_host()) to serialize operations and commands, > as to confirm to the SD/SDIO/(e)MMC specs. The above changes gives no > guarantees for this. To make that work, we would need a "mmc bus lock" > to be managed by the core. > > However, inventing a "mmc bus lock" would lead to other problems > related to I/O scheduling for upper layers - it simply breaks. For > example, I/O requests for one card/slot can then starve I/O requests > reaching another card/slot. So are you saying that multi-slot support is a no go in general or it is only applicable to DW MMC (I really doubt that's a case)? BTW there're other controllers that seem to support multi-slot like Atmel etc. -Alexey From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey.Brodkin@synopsys.com (Alexey Brodkin) Date: Fri, 20 Apr 2018 07:42:13 +0000 Subject: [RFC 0/2] dw_mmc: add multislot support In-Reply-To: References: <20180417121130.25281-1-Eugeniy.Paltsev@synopsys.com> Message-ID: <1524210132.4614.4.camel@synopsys.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Ulf, On Fri, 2018-04-20 at 09:35 +0200, Ulf Hansson wrote: > [...] > > > > > 2. Add missing stuff to support multislot mode in DesignWare MMC driver. > > * Add missing slot switch to __dw_mci_start_request() function. > > * Refactor set_ios function: > > a) Calculate common clock which is > > suitable for all slots instead of directly use clock value > > provided by mmc core. We calculate common clock as the minimum > > among each used slot clocks. This clock is calculated in > > dw_mci_calc_common_clock() function which is called > > from set_ios() > > b) Disable clock only if no other slots are ON. > > c) Setup clock directly in set_ios() only if no other slots > > are ON. Otherwise adjust clock in __dw_mci_start_request() > > function before slot switch. > > d) Move timings and bus_width setup to separate funcions. > > * Use timing field in each slot structure instead of common field in > > host structure. > > * Add locks to serialize access to registers. > > Sorry, but this is a hack to *try* to make multi-slot work and this > isn't sufficient. There were good reasons to why the earlier > non-working multi slot support was removed from dw_mmc. > > Let me elaborate a bit for your understanding. The core uses a host > lock (mmc_claim|release_host()) to serialize operations and commands, > as to confirm to the SD/SDIO/(e)MMC specs. The above changes gives no > guarantees for this. To make that work, we would need a "mmc bus lock" > to be managed by the core. > > However, inventing a "mmc bus lock" would lead to other problems > related to I/O scheduling for upper layers - it simply breaks. For > example, I/O requests for one card/slot can then starve I/O requests > reaching another card/slot. So are you saying that multi-slot support is a no go in general or it is only applicable to DW MMC (I really doubt that's a case)? BTW there're other controllers that seem to support multi-slot like Atmel etc. -Alexey