On Thu, May 20, 2021 at 12:58 AM Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxx> wrote: > > On 19/05/2021 04:07, Stephan Gerhold wrote: > > On Tue, May 18, 2021 at 11:25:55AM -0400, Krzysztof Kozlowski wrote: > >> On 18/05/2021 11:00, Stephan Gerhold wrote: > >>> On Tue, May 18, 2021 at 10:30:43AM -0400, Krzysztof Kozlowski wrote: > >>>> On 18/05/2021 09:39, Stephan Gerhold wrote: > >>>>> s3fwrn5 has a NFC_CLK_REQ output GPIO, which is asserted whenever > >>>>> the clock is needed for the current operation. This GPIO can be either > >>>>> connected directly to the clock provider, or must be monitored by > >>>>> this driver. > >>>>> > >>>>> As an example for the first case, on many Qualcomm devices the > >>>>> NFC clock is provided by the main PMIC. The clock can be either > >>>>> permanently enabled (clocks = <&rpmcc RPM_SMD_BB_CLK2>) or enabled > >>>>> only when requested through a special input pin on the PMIC > >>>>> (clocks = <&rpmcc RPM_SMD_BB_CLK2_PIN>). > >>>>> > >>>>> On the Samsung Galaxy A3/A5 (2015, Qualcomm MSM8916) this mechanism > >>>>> is used with S3FWRN5's NFC_CLK_REQ output GPIO to enable the clock > >>>>> only when necessary. However, to make that work the s3fwrn5 driver > >>>>> must keep the RPM_SMD_BB_CLK2_PIN clock enabled. > >>>> > >>>> This contradicts the code. You wrote that pin should be kept enabled > >>>> (somehow... by driver? by it's firmware?) but your code requests the > >>>> clock from provider. > >>>> > >>> > >>> Yeah, I see how that's a bit confusing. Let me try to explain it a bit > >>> better. So the Samsung Galaxy A5 (2015) has a "S3FWRN5XS1-YF30", some > >>> variant of S3FWRN5 I guess. That S3FWRN5 has a "XI" and "XO" pin in the > >>> schematics. "XO" seems to be floating, but "XI" goes to "BB_CLK2" > >>> on PM8916 (the main PMIC). > >>> > >>> Then, there is "GPIO2/NFC_CLK_REQ" on the S3FWRN5. This goes to > >>> GPIO_2_NFC_CLK_REQ on PM8916. (Note: I'm talking about two different > >>> GPIO2 here, one on S3FWRN5 and one on PM8916, they just happen to have > >>> the same number...) > >>> > >>> So in other words, S3FWRN5 gets some clock from BB_CLK2 on PM8916, > >>> and can tell PM8916 that it needs the clock via GPIO2/NFC_CLK_REQ. > >>> > >>> Now the confusing part is that the rpmcc/clk-smd-rpm driver has two > >>> clocks that represent BB_CLK2 (see include/dt-bindings/clock/qcom,rpmcc.h): > >>> > >>> - RPM_SMD_BB_CLK2 > >>> - RPM_SMD_BB_CLK2_PIN > >>> > >>> (There are also *_CLK2_A variants but they are even more confusing > >>> and not needed here...) > >>> > >>> Those end up in different register settings in PM8916. There is one bit > >>> to permanently enable BB_CLK2 (= RPM_SMD_BB_CLK2), and one bit to enable > >>> BB_CLK2 based on the status of GPIO_2_NFC_CLK_REQ on PM8916 > >>> (= RPM_SMD_BB_CLK2_PIN). > >>> > >>> So there is indeed some kind of "AND" inside PM8916 (the register bit > >>> and "NFC_CLK_REQ" input pin). To make that "AND" work I need to make > >>> some driver (here: the s3fwrn5 driver) enable the clock so the register > >>> bit in PM8916 gets set. > >> > >> Thanks for the explanation, it sounds good. The GPIO2 (or how you call > >> it NFC_CLK_REQ) on S3FWRN5 looks like non-configurable from Linux point > >> of view. Probably the device firmware plays with it always or at least > >> handles it in an unknown way for us. > >> > > > > FWIW, I was looking at some more s3fwrn5 code yesterday and came > > across this (in s3fwrn5_nci_rf_configure()): > > > > /* Set default clock configuration for external crystal */ > > fw_cfg.clk_type = 0x01; > > fw_cfg.clk_speed = 0xff; > > fw_cfg.clk_req = 0xff; > > ret = nci_prop_cmd(info->ndev, NCI_PROP_FW_CFG, > > sizeof(fw_cfg), (__u8 *)&fw_cfg); > > if (ret < 0) > > goto out; > > > > It does look quite suspiciously like that configures how s3fwrn5 expects > > the clock and possibly (fw_cfg.clk_req?) how GPIO2 behaves. But it's not > > particularly useful without some documentation for the magic numbers. > > Right, without documentation of FW protocol there is not much we can > deduct here. There is no proof even that the comment matches actual code. > > Dear Bongsu, > Maybe you could share some details about clock selection? These configuration values depend on the HW circuit for NFC. There are two types of fw_cfg.clk_type for N5. 0x01 : external XTAL ( don't need to control the clock because XTAL always supplies the NFC clock automatically.) 0x00 : PLL clock (need to control clock. ) There are three types of fw_cfg.clk_speed for N5. 0xFF : for external XTAL 0x00 : 24M for PLL. 0x01 : 19.12M for PLL. There are two types of fw_cfg.clk_req for N5. 0xFF: NFC firmware controls CLK Req when NFC needs the external clock. 0xF0: NFC firmware doesn't control CLK Req. > > > > > Personally, I just skip all firmware/RF configuration (which works thanks > > to commit 4fb7b98c7be3 ("nfc: s3fwrn5: skip the NFC bootloader mode")). > > That way, S3FWRN5 just continues using the proper configuration > > that was loaded by the vendor drivers at some point. :) > > But isn't that configuration lost after power off? > If you skip all firmware/RF configuration, you can use the preserved firmware and RF configuration on the chip. > > Best regards, > Krzysztof