On Wed, May 10, 2023 at 6:26 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > Re subject, what does the patch actually *do*? > > It looks like it "asserts PERST# on BCM2711", which I think would be > more informative than "don't assume 2711 bootloader leaves PERST# > asserted". Do you have any other feedback on the other commits? I can change the subject message as you like and the remove the stale footnote you and Cyril noticed, and submit V6. Thanks, Jim Quinlan Broadcom STB > > On Mon, May 08, 2023 at 06:01:24PM -0400, Jim Quinlan wrote: > > The current PCIe driver assumes PERST# is asserted when probe() is invoked. > > The reasons are as follows: > > > > (1) One Broadcom SOC (7278) causes a panic if the PERST# register is > > written during this time window. > > > > (2) If PERST# is deasserted at Linux probe() time, experience and QA > > suspend/resume tests have shown that some endpoint devices fail if the > > PERST# is pulsed (deasserted => asserted => deasserted) quickly in this > > fashion, even though the timing is in accordance with their datasheets. > > > > (3) Keeping things in reset tends to save power, if for some reason the > > PCIe driver is not yet present. > > > > Broadcom STB and CM SOCs bootloaders always have PERST# asserted at > > probe(). This is not necessarily the case for the 2711/RPi bootloader, > > so, for 2711/RPi SOCs, do what Raspian OS does and assert PERST#. > > > > [1] https://lore.kernel.org/linux-pci/20230411165919.23955-1-jim2101024@xxxxxxxxx/T/#m39ebab8bc2827b2304aeeff470a6c6a58f46f987 > > Does this link go with something above? "[1]" isn't mentioned above. > I did look at that message, but the connection to this patch isn't > obvious to me. > > > Signed-off-by: Jim Quinlan <jim2101024@xxxxxxxxx> > > --- > > drivers/pci/controller/pcie-brcmstb.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c > > index fe0415a98c63..7b698a9a851e 100644 > > --- a/drivers/pci/controller/pcie-brcmstb.c > > +++ b/drivers/pci/controller/pcie-brcmstb.c > > @@ -884,6 +884,11 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie) > > > > /* Reset the bridge */ > > pcie->bridge_sw_init_set(pcie, 1); > > + > > + /* Ensure that PERST# is asserted; some bootloaders may deassert it. */ > > + if (pcie->type == BCM2711) > > + pcie->perst_set(pcie, 1); > > + > > usleep_range(100, 200); > > > > /* Take the bridge out of reset */ > > -- > > 2.17.1 > >
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