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

[sathyanarayanan kuppuswamy]

On 03/17/2017 10:50 AM, Guenter Roeck wrote:
> 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@xxxxxxxxxxxxxxx>
> > > > > ---
> > > > > 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 ?
Sorry, It looks like I missed your point in your previous email.  I 
thought that gcs_pmc mem resource will be used only if watchdog device 
is enumerated by intel_pmc_ipc.c

After reviewing the code again, I found out this iTCO_wdt driver can 
also be enumerated by drivers/mfd/lpc_ich.c and 
drivers/i2c/busses/i2c-i801.c. Both these drivers pass the GCS as memory 
resource. So using intel_pmc_ipc specific calls will break watchdog 
functionality if its enumerated by any device other than intel_pmic_ipc.c

May be I should add a flag for ipc case in itco_wdt_platform_data and 
handle this as a special case.
> > 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

--
Sathyanarayanan Kuppuswamy
Android kernel developer