Hi Lukasz, Às 9:44 PM de 1/16/2017, Lukasz Majewski escreveu: > Hi Joao, > >> >> Hi, >> >> Às 10:13 AM de 1/16/2017, Kishon Vijay Abraham I escreveu: >>> + Joao, Jingoo >>> >>> Hi, >>> >>> On Monday 16 January 2017 03:01 PM, Lukasz Majewski wrote: >>>> Hi Kishon, >>>> >>>>> Hi Łukasz, >>>>> >>>>> On Monday 16 January 2017 12:19 PM, Lukasz Majewski wrote: >>>>>> Hi Kishon, >>>>>> >>>>>>> Hi, >>>>>>> >>>>>>> On Sunday 15 January 2017 06:49 PM, Lukasz Majewski wrote: >>>>>>>> Some devices (due to e.g. bad PCIe signal integrity) require to >>>>>>>> run with forced GEN1 speed on PCIe bus. >>>>>>>> >>>>>>>> This patch changes the speed explicitly on dra7 based devices >>>>>>>> when proper device tree attribute is defined for the PCIe >>>>>>>> controller. >>>>>>>> >>>>>>>> Signed-off-by: Lukasz Majewski <lukma@xxxxxxx> >>>>>>> >>>>>>> Bjorn has already queued a patch to do the same thing >>>>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_cgit_linux_kernel_git_helgaas_pci.git_log_-3Fh-3Dpci_host-2Ddra7xx&d=DwIDaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=s2fO0hii0OGNOv9qQy_HRXy-xAJUD1NNoEcc3io_kx0&m=zD82T5n4WcL7Ga-NSY2NI7KE75xQ99hN-mW2yX46wQk&s=E8zk1CbKxGH-f3fw_WpXxFU-A8BLkgA8NusCaxk1SvA&e= >>>>>> >>>>>> It seems like Bjorn only modifies CAP registers. >>>>> >>>>> The patch also modifies the LNKCTL2 register. >>>>>> >>>>>> He also needs to change register with 0x080C offset to actually >>>>>> ( PCIECTRL_PL_WIDTH_SPEED_CTL ) >>>>> >>>>> This bit is used to initiate speed change (after the link is >>>>> initialized in GEN1). Resetting the bit (like what you have done >>>>> here) prevents speed change. >>>> >>>> This is strange, but e2e advised me to do things as I did in the >>>> patch to _force_ GEN1 operation on PCIe2 port [1] (AM5728) >>>> >>>> Link: >>>> [1] >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__e2e.ti.com_support_arm_sitara-5Farm_f_791_t_566421&d=DwIDaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=s2fO0hii0OGNOv9qQy_HRXy-xAJUD1NNoEcc3io_kx0&m=zD82T5n4WcL7Ga-NSY2NI7KE75xQ99hN-mW2yX46wQk&s=uXLwglyRYqKpwp1JSxkOWmKpQ2wjfhgofpm8DCfquNw&e= >>>> >>>> Both patches modify 0x5180 007C register to set GEN1 capability >>>> (PCI_EXP_LNKCAP_SLS_2_5GB) >>>> >>>> The problem is with second register (in your patch): >>>> >>>> From SPRUHZ6G TRM: >>>> >>>> PCIECTRL_EP_DBICS_LNK_CAS_2 (0x5180 00A0) >>>> - TRGT_LINK_SPEED (Reset 0x1) - "Target Link Speed" - no more >>>> description in TRM >>>> >>>> It is set to PCI_EXP_LNKCAP_SLS_2_5GB = 0x1, which is the same as >>>> default /reset value. >>> >>> The default value is 0x2 (or else none of the cards would have >>> enumerated in GEN2) >>>> >>>> >>>> Could you clarify which way to _force_ PCIe GEN1 operation is >>>> correct? Mine shows differences in lspci output (as posted in [1]). >>> >>> You'll see the difference even with the patch in Bjorn's tree ;-) >>> >>> I think these are 2 different approaches to keep the link at GEN1. >>> Joao or Jingoo, do you have any suggestion here? >> >> I studied the Databook, > > Could you reveal which databook do you have in mind? Is that the TRM for > AM5728? I checked the Designware PCIe Databook, since it is based on this IP. > >> and both approaches seem to be right, >> dependently of the Core configuration and setup. >> >> The standard manual speed change sequence is: >> a) Write to PCIE_CAP_TARGET_LINK_SPEED (indicating desired speed) > > Do you mean TRGT_LINK_SPEED @ 0x5180 00A0 ? Correct. > >> b) Clear "Directed Speed Change" > > CFG_DIRECTED_SPEED_CHANGE @ 0x5180 080C Correct. > >> c) Set "Directed Speed Change" >> >> If "Directed Speed Change" is set (DEFAULT_GEN2_SPEED_CHANGE is the >> default value), it will execute LTSSM to initiate speed change to >> Gen2 or Gen3, after link is started in Gen1, and then the bit is >> automatically cleared. > > Ok, so with default settings (after reset) we do have Gen1 speed link > and when we enable LTSSM (with LTSSM_EN bit setting) we negotiate to > Gen2/Gen3. Yes, that's the expected behavior. I submited this direct question to R&D and will have your doubt answered soon. > >> >> Lukasz is reseting this bit, in order to avoid the LTSSM to be >> executed, which is correct. > > So with CFG_DIRECTED_SPEED_CHANGE = 0, when I start LTSSM (with > LTSSM_EN) the state machine returns immediately and leaves link in the > Gen1? > > The pci-dra7 driver always sets LTSSM_EN bit to start link negotiation. > >> There is another way to prevent this >> automatic speed change, which is to set GEN1 speed before link up >> which might be difficult in some setups, so Kishon's also right. >> >> In my opinion Lukasz approach would be the one that might be more >> universal and more "secure". > > The robustness is the key here since there are some devices, which on > particular HW must only work with Gen1 speed. When we start LTSSM state > machine and hence start negotiation to Gen2, not always the result of > LTSSM is correct and device is properly recognized. > >> >> Joao >> >> >>> >>>> >>>>> >>>>> IMO the better way is to set the LNKCTL2 to GEN1 instead of >>>>> hacking the IP register. >>>> >>>> From the original patch description: >>>> >>>> "Add support to force Root Complex to work in GEN1 mode if so >>>> desired, but don't force GEN1 mode on any board just yet." >>>> >>>> Are there any (floating around) patches allowing forcing GEN1 >>>> operation on any board (I would like to reuse/port them to my >>>> current solution)? >>> >>> For setting to GEN1 mode, "max-link-speed" should be set to 1 in dt >>> with the patch in Bjorn's tree. >>> >>> Thanks >>> Kishon >>> >> > > Best regards, > > Lukasz Majewski > > -- > > DENX Software Engineering GmbH, Managing Director: Wolfgang Denk > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany > Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@xxxxxxx > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
