--- /dev/null
+From: Catalin Marinas <catalin.marinas@arm.com>
+Subject: Re: [PATCH] ARM: vfp: Always save VFP state in vfp_pm_suspend
+Date: Mon, 14 Feb 2011 11:42:22 +0000
+Organization: ARM Limited
+Lines: 43
+Message-ID: <1297683742.30092.11.camel@e102109-lin.cambridge.arm.com>
+References: <1297638813-1315-1-git-send-email-ccross@android.com>
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+Cc: linux-arm-kernel@lists.infradead.org,
+ Russell King <linux@arm.linux.org.uk>,
+ linux-kernel@vger.kernel.org
+To: Colin Cross <ccross@android.com>
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+
+On Sun, 2011-02-13 at 23:13 +0000, Colin Cross wrote:
+> vfp_pm_suspend should save the VFP state any time there is
+> a last_VFP_context. If it only saves when the VFP is enabled,
+> the state can get lost when, on a UP system:
+> Thread 1 uses the VFP
+> Context switch occurs to thread 2, VFP is disabled but the
+> VFP context is not saved to allow lazy save and restore
+> Thread 2 initiates suspend
+> vfp_pm_suspend is called with the VFP disabled, but the
+> context has not been saved.
+
+At this point is it guaranteed that the thread won't migrate to another
+CPU? If not, we should use get/put_cpu.
+
+> --- a/arch/arm/vfp/vfpmodule.c
+> +++ b/arch/arm/vfp/vfpmodule.c
+> @@ -415,13 +415,12 @@ static int vfp_pm_suspend(struct sys_device *dev, pm_message_t state)
+> struct thread_info *ti = current_thread_info();
+> u32 fpexc = fmrx(FPEXC);
+>
+> - /* if vfp is on, then save state for resumption */
+> - if (fpexc & FPEXC_EN) {
+> + /* save state for resume */
+> + if (last_VFP_context[ti->cpu]) {
+> printk(KERN_DEBUG "%s: saving vfp state\n", __func__);
+> - vfp_save_state(&ti->vfpstate, fpexc);
+> -
+> - /* disable, just in case */
+> - fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
+> + fmxr(FPEXC, fpexc | FPEXC_EN);
+> + vfp_save_state(last_VFP_context[ti->cpu], fpexc);
+> + fmxr(FPEXC, fpexc & ~FPEXC_EN);
+> }
+
+We may want to set the last_VFP_context to NULL so that after resuming
+(to the same thread) we force the VFP reload from the vfpstate
+structure. The vfp_support_entry code ignores the reloading if the
+last_VFP_context is the same as vfpstate.
+
+--
+Catalin
+
+
+
+
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