From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: Revert "dmaengine: pl330: add DMA_PAUSE feature" From: Vinod Koul Message-Id: <20180509065922.GC7985@vkoul-mobl> Date: Wed, 9 May 2018 12:29:22 +0530 To: Frank Mori Hess Cc: Marek Szyprowski , Vinod Koul , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, Dan Williams , r.baldyga@hackerion.com, Krzysztof Kozlowski , Bartlomiej Zolnierkiewicz List-ID: T24gMDgtMDUtMTgsIDEwOjM2LCBGcmFuayBNb3JpIEhlc3Mgd3JvdGU6Cj4gT24gVHVlLCBNYXkg OCwgMjAxOCBhdCA1OjA0IEFNLCBNYXJlayBTenlwcm93c2tpCj4gPG0uc3p5cHJvd3NraUBzYW1z dW5nLmNvbT4gd3JvdGU6Cj4gPiBIaSBGcmFuayBhbmQgVmlub2QsCj4gPgo+ID4gT24gMjAxOC0w NC0yOCAyMzo1MCwgRnJhbmsgTW9yaSBIZXNzIHdyb3RlOgo+ID4+IFRoaXMgcmV2ZXJ0cyBjb21t aXQgODg5ODdkMmM3NTM0YTAyNjlmNTY3ZmIxMDFlNmQ3MWEwOGYwZjAxZC4KPiA+Pgo+ID4+IFRo ZSBwbDMzMC5jIHBhdXNlIGltcGxlbWVudGF0aW9uIHZpb2xhdGVzIHRoZSBkbWFlbmdpbmUgcmVx dWlyZW1lbnQKPiA+PiBmb3Igbm8gZGF0YSBsb3NzLCBzaW5jZSBpdCByZWxpZXMgb24gdGhlIERN QUtJTEwKPiA+PiBpbnN0cnVjdGlvbi4gIEhvd2V2ZXIsIERNQUtJTEwgZGlzY2FyZHMgaW4tZmxp Z2h0IGRhdGEgZnJvbSB0aGUKPiA+PiBkbWEgY29udHJvbGxlcidzIGZpZm8uICBUaGlzIGlzIGRv Y3VtZW50ZWQgaW4gdGhlIGRtYS0zMzAgbWFudWFsCj4gPj4gYW5kIEkgaGF2ZSBvYnNlcnZlZCBp dCB3aXRoIGhhcmR3YXJlIGRvaW5nIGRldmljZS10by1tZW1vcnkgYnVyc3QKPiA+PiB0cmFuc2Zl cnMuICBUaGUgZGlzY2FyZGVkIGRhdGEgbWF5IG9yIG1heSBub3Qgc2hvdyB1cCBpbiB0aGUKPiA+ PiByZXNpZHVlIGNvdW50LCBkZXBlbmRpbmcgb24gdGltaW5nIChyZXN1bHRpbmcgaW4gZGF0YSBj b3JydXB0aW9uCj4gPj4gZWZmZWN0aXZlbHkpLgo+ID4+Cj4gPj4gU2lnbmVkLW9mZi1ieTogRnJh bmsgTW9yaSBIZXNzIDxmbWg2ampAZ21haWwuY29tPgo+ID4KPiA+IFRoaXMgcmV2ZXJ0IGNvbXBs ZXRlbHkgYnJlYWtzIHNlcmlhbCBkcml2ZXIgb3BlcmF0aW9uIG9uIGFsbW9zdCBhbGwgRXh5bm9z Cj4gPiBTb0NzLCBiZWNhdXNlIHNlcmlhbCBkcml2ZXIgcmVsaWVzIG9uIGhhdmluZyBQQVVTRSBm ZWF0dXJlIGFuZCBwcm9wZXIKPiA+IHJlc2lkdWUgcmVwb3J0aW5nIGZyb20gZG1hIGVuZ2luZS4g UGxlYXNlIGRyb3AgaXQgaWYgcG9zc2libGUuCgpIaSBNYXJlaywKCkkgd291bGQgYXBwcmVjaWF0 ZSBpZiB5b3UgY2FuIHJldmlldyB0aGUgcGwzMzAgY2hhbmdlcyBhcyB0aGF0IGNsZWFybHkgc2Vl bXMgdG8KaW1wYWN0IHlvdS4gVGhpcyB3YXMgaW4gcmV2aWV3IGZvciBxdWl0ZSBhIGJpdAoKPiBJ dCB3aWxsIGNhdXNlIHRoZSBzZXJpYWwgZHJpdmVyIHRvIG5vdCB1c2UgdGhlIHBsMzMwLmMgZHJp dmVyIGZvciBkbWEsCj4gdGhlIHNlcmlhbCBkcml2ZXIgd2lsbCBmYWxsIGJhY2sgb24gdXNpbmcg dGhlIGNwdS4gIFRoaXMgaXMKPiB1bmZvcnR1bmF0ZSwgYnV0IHRoZSBkbWEgaGFyZHdhcmUgc2lt cGx5IGRvZXMgbm90IHN1cHBvcnQgcGF1c2UuICBUaGUKPiAibmljZSIgc3RvcCBpbnN0cnVjdGlv biBETUFFTkQgaXMgbm90IGFsbG93ZWQgdG8gYmUgaW5zZXJ0ZWQgdXNpbmcgdGhlCj4gZGVidWcg aW5zdHJ1Y3Rpb24gcmVnaXN0ZXIuICBUaGUgb25seSBwb3NzaWJpbGl0eSBmb3IgaW1wbGVtZW50 aW5nCj4gcGF1c2Ugd291bGQgYmUgdG8gbWFrZSB0aGUgZG1hIHRyYW5zZmVyIGRvIGEgRE1BV0ZF ICh3YWl0IGZvciBldmVudCkKPiBiZWZvcmUgZXZlcnkgdHJhbnNmZXIuICBUaGVuIHlvdSB3b3Vs ZCBuZWVkIHRvIGRldm90ZSBhbm90aGVyIGRtYQo+IHRocmVhZCB0byBkb2luZyBub3RoaW5nIGJ1 dCBETUFTRVYgKHNlbmQgZXZlbnQpIHRvIGtlZXAgdGhlIHRyYW5zZmVyCj4gZ29pbmcuICBUaGUg cGF1c2UgY291bGQgdGhlbiBETUFLSUxMIHRoZSBldmVudC1nZW5lcmF0aW5nIHRocmVhZAo+IHJh dGhlciB0aGFuIHRoZSB0cmFuc2ZlciB0aHJlYWQuICBJIGRvbid0IGtub3cgZXhhY3RseSB3aGF0 IHRoZQo+IHBlcmZvcm1hbmNlIGltcGFjdCB3b3VsZCBiZSwgYnV0IGl0IGNvdWxkbid0IGJlIGdv b2QuCj4gCj4gVGhlIHNlcmlhbCBkcml2ZXIgY291bGQgYmUgbW9kaWZpZWQgdG8gc3RpbGwgdXNl IGRtYSBmb3IgVFgsIHNpbmNlIGl0Cj4gb25seSBuZWVkcyBwYXVzZSBmb3IgUlguICBBbHNvLCBp ZiB5b3VyIHNlcmlhbCBoYXJkd2FyZSBjYW4gcmVwb3J0Cj4gZXhhY3RseSBob3cgbWFueSBieXRl cyBpdCBoYXMgc2l0dGluZyBpbiBpdHMgcnggZmlmbywgdGhlIHNlcmlhbAo+IGRyaXZlciBjb3Vs ZCBiZSBtb2RpZmllZCB0byB1c2UgcGF1c2UtbGVzcyBkbWEgZm9yIFJYLiAgVGhpcyBpcwo+IGFj dHVhbGx5IHdoYXQgSSBkaWQgZm9yIHRoZSBjdXN0b20gc2VyaWFsIGhhcmR3YXJlIEknbSB1c2lu ZyB3aXRoIGEKPiBkbWEtMzMwLCBhbHRob3VnaCBvdXIgc2VyaWFsIGhhcmR3YXJlIGhhcyBhIHZl cnkgbGFyZ2UgcnggZmlmbyB3aGljaAo+IG1ha2VzIHRoaXMgc2NoZW1lIHdvcnRod2hpbGUuCgpU aGF0IG1ha2VzIHNlbnNlIHRvIG1lLiBJZiBkbWEgZG9lc250IHN1cHBvcnQsIHRoZW4gd2h5IHNo b3VsZCBTVyBjbGFpbSBicm9rZW4Kc3VwcG9ydC4uCg== From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756126AbeEIG71 (ORCPT ); Wed, 9 May 2018 02:59:27 -0400 Received: from mail-pl0-f44.google.com ([209.85.160.44]:44814 "EHLO mail-pl0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753289AbeEIG7Z (ORCPT ); Wed, 9 May 2018 02:59:25 -0400 X-Google-Smtp-Source: AB8JxZoEo2lUlS0cO3RRk9LE3Z8O2DMVZ2oS/NxVJFRmT433Yl5LK7yEIHnnwVK4JK+xNMYyPq2zgw== Date: Wed, 9 May 2018 12:29:22 +0530 From: Vinod Koul To: Frank Mori Hess Cc: Marek Szyprowski , Vinod Koul , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, Dan Williams , r.baldyga@hackerion.com, Krzysztof Kozlowski , Bartlomiej Zolnierkiewicz Subject: Re: Revert "dmaengine: pl330: add DMA_PAUSE feature" Message-ID: <20180509065922.GC7985@vkoul-mobl> References: <2484918.HKVQc3yJkt@bear> <53b13d76-16a1-0e0a-09e1-c917e5d49326@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08-05-18, 10:36, Frank Mori Hess wrote: > On Tue, May 8, 2018 at 5:04 AM, Marek Szyprowski > wrote: > > Hi Frank and Vinod, > > > > On 2018-04-28 23:50, Frank Mori Hess wrote: > >> This reverts commit 88987d2c7534a0269f567fb101e6d71a08f0f01d. > >> > >> The pl330.c pause implementation violates the dmaengine requirement > >> for no data loss, since it relies on the DMAKILL > >> instruction. However, DMAKILL discards in-flight data from the > >> dma controller's fifo. This is documented in the dma-330 manual > >> and I have observed it with hardware doing device-to-memory burst > >> transfers. The discarded data may or may not show up in the > >> residue count, depending on timing (resulting in data corruption > >> effectively). > >> > >> Signed-off-by: Frank Mori Hess > > > > This revert completely breaks serial driver operation on almost all Exynos > > SoCs, because serial driver relies on having PAUSE feature and proper > > residue reporting from dma engine. Please drop it if possible. Hi Marek, I would appreciate if you can review the pl330 changes as that clearly seems to impact you. This was in review for quite a bit > It will cause the serial driver to not use the pl330.c driver for dma, > the serial driver will fall back on using the cpu. This is > unfortunate, but the dma hardware simply does not support pause. The > "nice" stop instruction DMAEND is not allowed to be inserted using the > debug instruction register. The only possibility for implementing > pause would be to make the dma transfer do a DMAWFE (wait for event) > before every transfer. Then you would need to devote another dma > thread to doing nothing but DMASEV (send event) to keep the transfer > going. The pause could then DMAKILL the event-generating thread > rather than the transfer thread. I don't know exactly what the > performance impact would be, but it couldn't be good. > > The serial driver could be modified to still use dma for TX, since it > only needs pause for RX. Also, if your serial hardware can report > exactly how many bytes it has sitting in its rx fifo, the serial > driver could be modified to use pause-less dma for RX. This is > actually what I did for the custom serial hardware I'm using with a > dma-330, although our serial hardware has a very large rx fifo which > makes this scheme worthwhile. That makes sense to me. If dma doesnt support, then why should SW claim broken support.. -- ~Vinod