+ 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://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/log/?h=pci/host-dra7xx >>> >>> 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://e2e.ti.com/support/arm/sitara_arm/f/791/t/566421 > > 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? > >> >> 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 -- 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
