Hi Rob, -----Original Message----- From: Rob Herring [mailto:robherri...@gmail.com] Sent: Friday, June 19, 2015 11:48 AM To: Ilya Faenson Cc: mar...@holtmann.org; Arend Van Spriel; devicetree@vger.kernel.org; linux-blueto...@vger.kernel.org Subject: Re: FW: [PATCH v4 1/4] Broadcom Bluetooth UART Device Tree bindings
On Thu, Jun 18, 2015 at 3:37 PM, Ilya Faenson <ifaen...@broadcom.com> wrote: > Hi Rob. > > -----Original Message----- > From: linux-bluetooth-ow...@vger.kernel.org > [mailto:linux-bluetooth-ow...@vger.kernel.org] On Behalf Of Rob Herring > Sent: Thursday, June 18, 2015 3:41 PM > To: Ilya Faenson > Cc: mar...@holtmann.org; Arend Van Spriel; devicetree@vger.kernel.org; > linux-blueto...@vger.kernel.org > Subject: Re: FW: [PATCH v4 1/4] Broadcom Bluetooth UART Device Tree bindings > > On Thu, Jun 18, 2015 at 1:54 PM, Ilya Faenson <ifaen...@broadcom.com> wrote: >> Hi Rob, > > Your emails are base64 encoded. They should be plain text for the list. > > IF: The Outlook is configured to respond in the sender's format. I therefore > respond in the encoding you've used. I assure you that that is not the case or I would be banished from lists by now. Outlook is generally incapable of correctly sending mails to lists. The reply header above is one aspect of that. The other problem is your replies don't get wrapped and prefixed properly. That could be my client I guess, but *all* other mails are fine. My sent mails have: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable IF: Unluckily, Outlook is what I am supposed to use. I post patches from the Ubuntu VM but I have the command line access to it only. >> -----Original Message----- >> From: Rob Herring [mailto:robherri...@gmail.com] >> Sent: Thursday, June 18, 2015 11:03 AM >> To: Ilya Faenson >> Cc: mar...@holtmann.org; Arend Van Spriel; devicetree@vger.kernel.org; >> linux-blueto...@vger.kernel.org >> Subject: Re: FW: [PATCH v4 1/4] Broadcom Bluetooth UART Device Tree bindings >> >> On Wed, Jun 17, 2015 at 6:11 PM, Ilya Faenson <ifaen...@broadcom.com> wrote: >>> + devicetree lists > > [...] > >>> diff --git a/Documentation/devicetree/bindings/net/bluetooth/btbcm.txt >>> b/Documentation/devicetree/bindings/net/bluetooth/btbcm.txt >>> new file mode 100644 >>> index 0000000..5dbcd57 >>> --- /dev/null >>> +++ b/Documentation/devicetree/bindings/net/bluetooth/btbcm.txt >>> @@ -0,0 +1,86 @@ >>> +btbcm >>> +------ >>> + >>> +Required properties: >>> + >>> + - compatible : must be "brcm,brcm-bt-uart". >> >> You need to describe the chip, not the interface. >> >> IF: This driver is for all Broadcom Bluetooth UART based chips. > > BT only chips? Most/many Broadcom chips are combo chips. I understand > the driver for BT is *mostly* separate from other chip functions like > WiFi, GPS and NFC, but the h/w is a single chip. I say most because > likely there are some parts shared: a voltage rail, reset line, or > power down line. I think some can do BT over the SDIO interface too, > so the interface may be shared. The DT is a description of the h/w > (i.e. what part # for a chip) and not a driver data structure. You > need to describe the whole chip in the binding. It is a Linux problem > if there needs to be multiple separate drivers. > > IF: Defining complete DT description for the Broadcom combo chips for > multiple interfaces is well beyond the scope of what I am doing. I just need > to define a DT node for the input and output GPIOs connected to the BT UART > chip. BT may or may not be part of the combo chip: it does not really matter > for this exercise. I thought I would take this opportunity to place some BT > device parameters into that node as well. If you're not comfortable with > this, I could just call it a "GPIO set" to avoid mentioning BT and UART at > all but it would make little sense. Still, I could consider it. Would you > have "GPIO set" recommendations? Alternatively, NFC Marvell code you're > referring to has parameters configured as Linux module parameters. I could do > the same too, avoiding this device tree discussion. Let me know. > I don't completely follow what you mean by "GPIO set", but I'm guessing that is not the right path. > Generally speaking (pontification hat on :-)), what you're trying to do > (description of the whole chip) is well beyond what say ACPI has done (I was > involved some in the BT ACPI exercise a few years ago). BT UART interface is > described in ACPI independently of other parts of the same combo chip. > Requirements like that slow down the DT development in my opinion as > companies are understandably reluctant to work with unrealistic goals. End of > pontification. :-) > ACPI and DT are very different models in terms of abstraction and governance. I'm not going to hash through all the details. I'm not necessarily saying we have to have a single node, but that is my default position. You have convince me that the functions are completely independent and I cannot judge that if you are completely ignoring the WiFi part. From Broadcom chips I've worked with, the supplies at least are shared (something ACPI does not expose). Perhaps we could fudge that and just require the same supply has to be connected to each half. I still worry there could be other internal inter-dependencies. Perhaps BT requires the SDIO clock to be active or something like that. Maybe not on Broadcom chips, but on other vendors and I have to care about them all. Let's step back to what I'm asking for: - A more specific compatible string. This should include the chip name/number. You may not need it today, but it is insurance in case you do find differences latter. The only impact is the match table in your driver. You can also have a less specific compatible string if you want that the driver can match on. IF: Okay, I can change that. - Changing the location of the node. The node hierarchy implicitly defines connections. You have a connection from the host UART to the BT device. This needs to be described. Whether splitting BT and WiFi nodes or not, I've already said it probably makes the most sense to put this under the host uart node. IF: Okay, I have just tried placing my node under the UART. The platform driver probe is no longer called then though. What am I doing wrong? Pasting the relevant snippet: IF: &uart1 { IF: status = "okay"; IF: ... IF: bcm4354_bt_uart: bcm4354-bt-uart { IF: compatible = "brcm,brcm4354-bt-uart"; IF: bt-wake-gpios = <&gpio4 30 GPIO_ACTIVE_HIGH>; IF: ... IF: }; IF: }; - Splitting the nodes. Here we are looking at doing either: serial@1234 { compatible = "some-soc-uart"; brcm43340 { compatible = "brcm,brcm43340"; sdio-host = <&soc-sdhost>; // BT props // WiFi props }; }; Or: serial@1234 { compatible = "some-soc-uart"; brcm43340 { compatible = "brcm,brcm43340-bt"; // BT props }; }; mmc@5678 { compatible = "some-soc-sdhci"; brcm43340@0 { reg = <0>; compatible = "brcm,brcm43340-wifi"; // WiFi props }; }; Or maybe it is the latter example but we just add phandle links between the 2 nodes. We haven't even considered what happens when a chip also has FM, NFC, and/or GPS. Nor have we considered how to describe the audio connection to the host processor, but we've got nothing common and that can probably come latter. We need to agree figuring all this out is needed. Otherwise, this whole conversation is a waste of time. IF: Appreciate the detailed elaborations. The latter example with phandle links sounds reasonable to me. I am afraid I'm not in a position to agree to everything though as I'm responsible for the BT only. Arend Van Spriel representing Broadcom WLAN has started talking to you: that's good. >> >>> + - tty : tty device connected to this Bluetooth device. >> >> "tty" is a bit of a Linuxism and "ttyS0" certainly is. Further, there >> is no guarantee which uart is assigned ttyS0. >> >> This should be a phandle to the connected uart if not a sub node of >> the uart. This is complicated since these chips have multiple host >> connections. It needs to go under either uart or SDIO host and have a >> reference back to the one it is not under. Given the SDIO interface is >> discoverable (although sideband gpios and regulators are not), I would >> put this under the uart node as that is never discoverable. >> >> As I've mentioned previously, there's several cases of bindings for >> UART slave devices being posted. This all needs to be coordinated to >> use a common structure. >> >> IF: This driver does not really access the UART. If just needs to have a >> string of some sort to map instances of the BlueZ protocol into platform >> devices to employ the right GPIOs and interrupts. I could use anything you >> recommend available through the tty_struct coming to the protocol from the >> BlueZ line discipline. Moreover, every end user platform I've ever dealt >> with in 16 years of working with Bluetooth had a single BT UART device. So >> these are really rare (typically test platforms) cases only. The mapping is >> not needed for most platforms at all. I suspect the right thing to do would >> be to make this parameter optional. The mapping would be done only if the >> parameter is present. I will use anything tty_struct derived you specify. >> Makes sense? > > > You've missed my point. I'm not talking about connecting multiple > devices to a UART at once. There are several instances of people > trying to add UART connected devices into DT[1][2]. My point is these > devices all need to have the DT binding done in a common way across > different platforms. Otherwise, we can not have common code to parse > the DT and find devices attached to a UART. > > IF: Chances are I was not clear enough. I was not talking about connecting > multiple devices to a UART. I was talking about connecting one Broadcom BT > device to one serial port and another Broadcom BT device to another serial > port (rare enough setup). I do understand your goals though. I would be happy > to participate in that exercise (subject to the management approval) once DT > has published the UART device parameters and the Linux bluetooth-next has > support for DT enumerated devices. I don’t see it happening soon though. > Marvell example you've referred me to has nothing of the sort. What do you > think of allowing us something to ship now with an understanding that we > would support your UART enumerated devices once they are published? Okay. Several people want to describe a connection between a host uart and a device connected to the uart (BT, NFC, GPS, etc.). You are doing this with your "tty" property. My goal and requirement is that this connection be described in DT in the same way regardless of the device attached. Just like all I2C device connections are described by being child nodes under the I2C host regardless of the type of I2C device attached. IF: All good points, Rob. I will certainly get rid of the tty property if I can make the child device idea work. My complication is in the need to map say the DT device parent (UART) into the tty_struct used by the Linux BlueZ protocol. Any ideas on how to implement that ? Many thanks! Rob
