Dear All, > + 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) SPRUHZ6G – October 2014 – Revised June 2016 - page 6313. Maybe TRM is not up to date? > > > > > > 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 ;-) :-) The details of my test cases and output are in the post [1]. > > I think these are 2 different approaches to keep the link at GEN1. > Joao or Jingoo, do you have any suggestion here? Please read through thread [1] [1] https://e2e.ti.com/support/arm/sitara_arm/f/791/t/566421 > > > > >> > >> 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. Ah.... ok. > > 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
