From b25bcf1bcaf6687991ae08dd76cd784bf9fe3d05 Mon Sep 17 00:00:00 2001 From: Thomas Petazzoni Date: Mon, 12 May 2014 16:11:40 +0200 Subject: ARM: mvebu: mvebu-soc-id: keep clock enabled if PCIe unit is enabled Since the mvebu-soc-id code in mach-mvebu/ was introduced, several users have noticed a regression: the PCIe card connected in the first PCIe interface is not detected properly. This is due to the fact that the mvebu-soc-id code enables the PCIe clock of the first PCIe interface, reads the SoC device ID and revision number (yes this information is made available as part of PCIe registers), and then disables the clock. However, by doing this, we gate the clock and therefore loose the complex PCIe configuration that was done by the bootloader. Unfortunately, as of today, the kernel is not capable of doing this complex configuration by itself, so we really need to keep the PCIe clock enabled. However, we don't want to keep it enabled unconditionally: if the PCIe interface is not enabled or PCI support is not compiled into the kernel, there is no reason to keep the PCIe clock running. This issue was discussed with Kevin Hilman, and the suggested solution was to make the mvebu-soc-id code keep the clock enabled in case it will be needed for PCIe. This is therefore the solution implemented in this patch. Long term, we hope to make the kernel more capable in terms of PCIe configuration for this platform, which will anyway be needed to support the compilation of the PCIe host controller driver as a module. In the mean time however, we don't have much other choice than to implement the currently proposed solution. Reported-by: Neil Greatorex Cc: Neil Greatorex Cc: Jason Gunthorpe Cc: Kevin Hilman Signed-off-by: Thomas Petazzoni Link: https://lkml.kernel.org/r/1399903900-29977-3-git-send-email-thomas.petazzoni@free-electrons.com Fixes: af8d1c63afcb ("ARM: mvebu: Add support to get the ID and the revision of a SoC") Cc: # 3.14+: 42a18d1cf484: ARM: mvebu: mvebu-soc-id: add missing clk_put() call Cc: # 3.14+ Acked-by: Gregory CLEMENT Tested-by: Gregory CLEMENT Tested-by: Andrew Lunn Tested-by: Willy Tarreau Signed-off-by: Jason Cooper --- arch/arm/mach-mvebu/mvebu-soc-id.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'arch/arm') diff --git a/arch/arm/mach-mvebu/mvebu-soc-id.c b/arch/arm/mach-mvebu/mvebu-soc-id.c index b52af6f4a0c6..09520e19b78e 100644 --- a/arch/arm/mach-mvebu/mvebu-soc-id.c +++ b/arch/arm/mach-mvebu/mvebu-soc-id.c @@ -108,8 +108,18 @@ static int __init mvebu_soc_id_init(void) iounmap(pci_base); res_ioremap: - clk_disable_unprepare(clk); - clk_put(clk); + /* + * If the PCIe unit is actually enabled and we have PCI + * support in the kernel, we intentionally do not release the + * reference to the clock. We want to keep it running since + * the bootloader does some PCIe link configuration that the + * kernel is for now unable to do, and gating the clock would + * make us loose this precious configuration. + */ + if (!of_device_is_available(child) || !IS_ENABLED(CONFIG_PCI_MVEBU)) { + clk_disable_unprepare(clk); + clk_put(clk); + } clk_err: of_node_put(child); -- cgit v1.2.3