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

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Date:   Fri, 17 Mar 2017 06:40:22 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     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 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.
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.

Guenter