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From: | Scott Wood |
Subject: | Re: [Qemu-ppc] [Qemu-devel] [PATCH v2]booke: timer: Deactivate timer for target_bit above 61 |
Date: | Mon, 10 Jun 2013 12:20:05 -0500 |
On 06/10/2013 09:26:18 AM, Alexander Graf wrote:
On 06/10/2013 02:47 PM, Bhushan Bharat-R65777 wrote:-----Original Message----- From: Andreas Färber [mailto:address@hidden Sent: Monday, June 10, 2013 5:43 PM To: Bhushan Bharat-R65777Cc: address@hidden; address@hidden; address@hidden; Wood Scott-B07421; Bhushan Bharat-R65777Subject: Re: [Qemu-devel] [PATCH v2]booke: timer: Deactivate timer fortarget_bit above 61So IIUC we can only allow 63 bits due to signedness, thus a maximum of(1<< 62), thus target_bit<= 61.Any chance at least the comment can be worded to explain that any better? Maybealso use (target-bit + 1>= 63) or period> INT64_MAX as condition?How about this:/* QEMU timer supports a maximum timer of INT64_MAX (0x7fffffff_ffffffff).* Run booke fit/wdog timer when* ((1ULL<< target_bit + 1)< 0x40000000_00000000), i.e target_bit = 61. * Also the time with this maximum target_bit (with current range of * CPU frequency PowerPC supports) will be many many years. So it is* pretty safe to stop the timer above this threshold. */How about/* This timeout will take years to trigger. Treat the timer as disabled. */
There should be at least a brief mention that it's because the QEMU timer can't handle larger values, with the detailed explanation in the changelog. A better lower bound on the number of years would be nice as well (e.g. "hundreds of years").
-Scott
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