linux-kernel - Re: [PATCH v2 3/4] watchdog: iTCO_wdt: Fix PMC GCR memory mapping failure

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Message-ID: <20170317175052.GA23030@roeck-us.net>
Date:   Fri, 17 Mar 2017 10:50:52 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>,
        andy@...radead.org, qipeng.zha@...el.com, dvhart@...radead.org,
        david.e.box@...ux.intel.com, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org,
        wim@...ana.be
Subject: Re: [PATCH v2 3/4] watchdog: iTCO_wdt: Fix PMC GCR memory mapping
 failure

On Fri, Mar 17, 2017 at 10:24:35AM -0700, sathyanarayanan kuppuswamy wrote:
> 
> 
> On 03/17/2017 06:40 AM, Guenter Roeck wrote:
> >On 03/17/2017 04:43 AM, Rajneesh Bhardwaj wrote:
> >>On Thu, Mar 16, 2017 at 05:41:35PM -0700, Kuppuswamy Sathyanarayanan
> >>wrote:
> >>>Currently, iTCO watchdog driver uses memory map to access
> >>>PMC_CFG GCR register. But the entire GCR address space is
> >>>already mapped in intel_scu_ipc driver. So remapping the
> >>
> >>intel_pmc_ipc driver.
> >>
> >>>GCR register in this driver causes the mem request failure in
> >>>iTCO_wdt probe function. This patch fixes this issue by
> >>>using PMC GCR read/write API's to access PMC_CFG register.
> >>>
> >>>Signed-off-by: Kuppuswamy Sathyanarayanan
> >>><sathyanarayanan.kuppuswamy@...ux.intel.com>
> >>>---
> >>> drivers/watchdog/iTCO_wdt.c | 31 +++++++------------------------
> >>> 1 file changed, 7 insertions(+), 24 deletions(-)
> >>>
> >>>diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
> >>>index 3d0abc0..31abfc5 100644
> >>>--- a/drivers/watchdog/iTCO_wdt.c
> >>>+++ b/drivers/watchdog/iTCO_wdt.c
> >>>@@ -68,6 +68,8 @@
> >>> #include <linux/io.h>            /* For inb/outb/... */
> >>> #include <linux/platform_data/itco_wdt.h>
> >>>
> >>>+#include <asm/intel_pmc_ipc.h>
> >>>+
> >>> #include "iTCO_vendor.h"
> >>>
> >>> /* Address definitions for the TCO */
> >>>@@ -94,12 +96,6 @@ struct iTCO_wdt_private {
> >>>     unsigned int iTCO_version;
> >>>     struct resource *tco_res;
> >>>     struct resource *smi_res;
> >>>-    /*
> >>>-     * NO_REBOOT flag is Memory-Mapped GCS register bit 5 (TCO
> >>>version 2),
> >>>-     * or memory-mapped PMC register bit 4 (TCO version 3).
> >>>-     */
> >>
> >>Better to retain this comment elsewhere.
> >>
> >>>-    struct resource *gcs_pmc_res;
> >>>-    unsigned long __iomem *gcs_pmc;
> >>>     /* the lock for io operations */
> >>>     spinlock_t io_lock;
> >>>     /* the PCI-device */
> >>>@@ -176,9 +172,9 @@ static void iTCO_wdt_set_NO_REBOOT_bit(struct
> >>>iTCO_wdt_private *p)
> >>>
> >>>     /* Set the NO_REBOOT bit: this disables reboots */
> >>>     if (p->iTCO_version >= 2) {
> >>>-        val32 = readl(p->gcs_pmc);
> >>>+        val32 = intel_pmc_gcr_read(PMC_GCR_PMC_CFG_REG);
> >>
> >>better to have protection and error handling, discussed in v2, 2/4.
> >>
> >>compiled and tested this on APL and i see iTCO_WDT driver loads fine.
> >>Since
> >>it impacts core WDT functionality, need to be thoroughly tested on
> >>various
> >>platforms.
> >>
> >
> >I don't think I (or the watchdog mailing list) was copied on the original
> >patch.
> Sorry. Its my mistake. I will fix it in next series update.
> >Major immediate concern is that this introduces a dependency on external
> >code.
> >The pmc_ipc driver's Kconfig entry states "This is not needed for PC-type
> >machines". I don't know where the function is introduced, but I hope this
> >change
> >does not require the pmc_ipc code to be present on such machines for the
> >watchdog
> >to work. It would be bad if it does. If it doesn't, it appears that the
> >function
> >should not be declared in asm/intel_pmc_ipc.h.
> It should not create any compile time dependency with INTEL_PMC_IPC config
> option. If INTEL_PMC_IPC_CONFIG is disabled, we use
> empty definitions for these calls defined in asm/intel_pmc_ipc.h
> 

So the watchdog driver would get an error if CONFIG_INTEL_PMC_IPC
is not defined ? And that is supposed to be acceptable ?

> But iTCO_wdt driver already has runtime dependency with INTEL_PMIC_IPC if
> its version iTCO_version >= 2.
> 
Unless I am missing something, there is no explicit dependency. AFAICS
the watchdog driver works just fine if INTEL_PMIC_IPC is not enabled,
and/or if it is built as module and the module is not loaded.

Maybe you mean that the watchdog driver doesn't load if the INTEL_PMIC_IPC
driver is loaded. That would be a bug, not a dependency.

Guenter