From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Agner Subject: Re: serial: imx: half-duplex RS485 operation with RTS active low Date: Mon, 16 Apr 2018 12:29:11 +0200 Message-ID: References: <0e88706a05a302201be396d2f03c3e9e@agner.ch> <20180416092257.frbmooduhm4zrhhl@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <20180416092257.frbmooduhm4zrhhl@pengutronix.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= Cc: s.hauer@pengutronix.de, baruch@tkos.co.il, linux-arm-kernel@lists.infradead.org, linux-serial@vger.kernel.org List-Id: linux-serial@vger.kernel.org T24gMTYuMDQuMjAxOCAxMToyMiwgVXdlIEtsZWluZS1Lw7ZuaWcgd3JvdGU6Cj4gSGkgU3RlZmFu LAo+IAo+IE9uIE1vbiwgQXByIDE2LCAyMDE4IGF0IDExOjE0OjMyQU0gKzAyMDAsIFN0ZWZhbiBB Z25lciB3cm90ZToKPj4gVXNpbmcgdXBzdHJlYW0gSSBub3RpY2VkIHRoYXQgUlMtNDg1IGRvZXMg bm90IHdvcmsgaW4gdGhlIGRlZmF1bHQKPj4gY29uZmlndXJhdGlvbiBmb3Igb3VyIHBsYXRmb3Jt cyAoVG9yYWRleCBBcGFsaXMvQ29saWJyaSkuIENsb3Nlcgo+IAo+IFRoaXMgaXMgYW4gaS5NWDY/ Cj4gCgpZZXMsIHNvcnJ5IGFib3V0IHRoYXQuCgpCdXQgSSB0aGluayBpdCBpcyBpLk1YIFVBUlQg c3BlY2lmaWMsIEkgbm90aWNlZCB0aGUgc2FtZSBiZWhhdmlvciBvbgppLk1YIDcgdG9vLgoKPj4g ZGVidWdnaW5nIHNob3dzIHRoYXQgaXQgaXMgcmVsYXRlZCB0byAic2VyaWFsOiBpbXg6IGRlZmF1 bHQgdG8gaGFsZgo+PiBkdXBsZXggcnM0ODUiLgo+Pgo+PiBXZSB1c2UgdGhlIGkuTVggVUFSVCBp biBEVEUgbW9kZSBhbmQgY29udHJvbCB0aGUgUlMtNDg1IHRyYW5zY2VpdmVyCj4+IHVzaW5nIHRo ZSBSVFMgc2lnbmFsIGluIGxvdy1hY3RpdmUgbW9kZS4KPj4KPj4gCXVhcnQtaGFzLXJ0c2N0czsK Pj4gCWZzbCxkdGUtbW9kZTsKPj4gCWxpbnV4LHJzNDg1LWVuYWJsZWQtYXQtYm9vdC10aW1lOwo+ PiAJcnM0ODUtcnRzLWFjdGl2ZS1sb3c7Cj4gCj4gVGhhdCBtZWFucyB5b3UncmUgbm90IHVzaW5n IGEgR1BJTyBmb3IgUlRTIHNpZ25hbGluZywgcmlnaHQ/Cj4gIAoKSSB1c2UgbmF0aXZlIFJUUyBj YXBhYmlsaXR5ICh3aGljaCBpcyBpbiBEVEUgbW9kZSB0aGUgQ1RTIHNpZ25hbC4uLikKCj4+IFVz aW5nIHRoaXMgc2V0dGluZyBsZWFkcyB0byB0aGUgUlRTIHNpZ25hbCBub3QgZ2V0dGluZyBhc3Nl cnRlZCAodGhlCj4+IG9zY2lsbG9zY29wZSBvbmx5IHNob3dzIGEgdmVyeSBzaG9ydCBmbHVrZSBi ZWZvcmUgdGhlIHN0YXJ0IGJpdCBpcwo+PiBzZW50KS4KCkp1c3QgRllJLCB0aGUgZmx1a2UgbG9v a3MgbGlrZSBhIHByb3BlciBhc3NlcnQsIGJ1dCBpdCBpcyByZWFsbHkgb25seQo1MG5zIHdpZGUu Cgo+Pgo+PiBIb3dldmVyLCB1c2luZwo+Pgo+PiAJdWFydC1oYXMtcnRzY3RzOwo+PiAJZnNsLGR0 ZS1tb2RlOwo+PiAJbGludXgscnM0ODUtZW5hYmxlZC1hdC1ib290LXRpbWU7Cj4+IAlyczQ4NS1y dHMtYWN0aXZlLWxvdzsKPj4gCXJzNDg1LXJ4LWR1cmluZy10eDsKPj4KPj4gQXNzZXJ0cyB0aGUg UlRTIHNpZ25hbCBsb3cgYWN0aXZlIGp1c3QgZmluZS4uLgo+Pgo+PiBJcyB0aGlzIGEga25vd24g cHJvYmxlbT8gQW55IGlkZWEgd2hlcmUgdGhhdCBjb3VsZCBjb21lIGZyb20/IEl0IGxvb2tzCj4+ IGFzIGlmIHRoZSByZWNlaXZlciBwYXJ0IGlzIGFjdHVhbGx5IGVuYWJsaW5nIFJUUy4uLj8KPiAK PiBXaGljaCBrZXJuZWwgdmVyc2lvbiBkbyB5b3UgdXNlPyBNeSBsYXRlc3QgcnM0ODUgcmVsYXRl ZCBwYXRjaGVzIHdlbnQKPiBpbnRvIHY0LjE3LXJjMS4gV2l0aCB0aGF0IEkgbWFuYWdlZCB0byBt YWtlIHJzNDg1IGhhbGYgZHVwbGV4IHdvcmsgb24KPiBzZXZlcmFsIGN1c3RvbWVyIGJvYXJkcy4K CkkgdXNlZCB2NC4xNy1yYzEuCgpJIG5vdGljZWQgeW91ciBjaGFuZ2VzLCBidXQgSSBpdCBzZWVt cyB0aGV5IG1ha2Ugbm8gZGlmZmVyZW5jZSwgbGFzdAp3ZWVrIEkgbm90aWNlZCB0aGUgc2FtZSBp c3N1ZSBpbiB2NC4xNi4KCkRvIHRob3NlIGN1c3RvbWVyIGJvYXJkcyB1c2UgRFRFIG1vZGU/Cgot LQpTdGVmYW4KCj4gCj4+IEFsc28sIGlzbid0IGVuYWJsaW5nIFJYIGV2ZW4gaW4gaGFsZi1kdXBs ZXggbW9kZSBxdWl0ZSBjb21tb24gaW4gb3JkZXIKPj4gdG8gZGV0ZWN0IGNvbGxpc2lvbnM/Cj4g Cj4gSSBkb24ndCBrbm93Lgo+IAoKUHJvYmFibHkgYWxzbyBkZXBlbmRzIG9uIHRoZSBleGFjdCB1 c2UgY2FzZSBhbmQgdGhlIHRyYW5zY2VpdmVyCmNvbmZpZ3VyYXRpb24uCgotLQpTdGVmYW4KCl9f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmxpbnV4LWFybS1r ZXJuZWwgbWFpbGluZyBsaXN0CmxpbnV4LWFybS1rZXJuZWxAbGlzdHMuaW5mcmFkZWFkLm9yZwpo dHRwOi8vbGlzdHMuaW5mcmFkZWFkLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2xpbnV4LWFybS1rZXJu ZWwK From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefan@agner.ch (Stefan Agner) Date: Mon, 16 Apr 2018 12:29:11 +0200 Subject: serial: imx: half-duplex RS485 operation with RTS active low In-Reply-To: <20180416092257.frbmooduhm4zrhhl@pengutronix.de> References: <0e88706a05a302201be396d2f03c3e9e@agner.ch> <20180416092257.frbmooduhm4zrhhl@pengutronix.de> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 16.04.2018 11:22, Uwe Kleine-K?nig wrote: > Hi Stefan, > > On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote: >> Using upstream I noticed that RS-485 does not work in the default >> configuration for our platforms (Toradex Apalis/Colibri). Closer > > This is an i.MX6? > Yes, sorry about that. But I think it is i.MX UART specific, I noticed the same behavior on i.MX 7 too. >> debugging shows that it is related to "serial: imx: default to half >> duplex rs485". >> >> We use the i.MX UART in DTE mode and control the RS-485 transceiver >> using the RTS signal in low-active mode. >> >> uart-has-rtscts; >> fsl,dte-mode; >> linux,rs485-enabled-at-boot-time; >> rs485-rts-active-low; > > That means you're not using a GPIO for RTS signaling, right? > I use native RTS capability (which is in DTE mode the CTS signal...) >> Using this setting leads to the RTS signal not getting asserted (the >> oscilloscope only shows a very short fluke before the start bit is >> sent). Just FYI, the fluke looks like a proper assert, but it is really only 50ns wide. >> >> However, using >> >> uart-has-rtscts; >> fsl,dte-mode; >> linux,rs485-enabled-at-boot-time; >> rs485-rts-active-low; >> rs485-rx-during-tx; >> >> Asserts the RTS signal low active just fine... >> >> Is this a known problem? Any idea where that could come from? It looks >> as if the receiver part is actually enabling RTS...? > > Which kernel version do you use? My latest rs485 related patches went > into v4.17-rc1. With that I managed to make rs485 half duplex work on > several customer boards. I used v4.17-rc1. I noticed your changes, but I it seems they make no difference, last week I noticed the same issue in v4.16. Do those customer boards use DTE mode? -- Stefan > >> Also, isn't enabling RX even in half-duplex mode quite common in order >> to detect collisions? > > I don't know. > Probably also depends on the exact use case and the transceiver configuration. -- Stefan