From: timur@codeaurora•org (Timur Tabi)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 2/3] [v4] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc
Date: Mon, 17 Aug 2015 18:56:10 -0500 [thread overview]
Message-ID: <55D2749A.401@codeaurora.org> (raw)
In-Reply-To: <20150810094008.GD1604@arm.com>
On 08/10/2015 04:40 AM, Will Deacon wrote:
>> >+static inline void __dcc_putchar(char c)
>> >+{
>> >+ asm volatile("msr dbgdtrtx_el0, %0"
>> >+ : /* No output register */
>> >+ : "r" (c));
>> >+ isb();
> I think we should be masking out the upper bits of c before the msr
> (the compiler probably expects a uxtb).
Well, we've never seen a problem, but that doesn't mean it doesn't
exist. I couldn't find anything in the ARMv8 ARM (section H9.2.7
DBGDTRTX_EL0) about word sizes.
Do you think that I need an explicit instruction to clear the upper
bits? I tried a few compiler tricks (e.g. "c && 0xff" and the like),
and they had no effect.
I do need help with the inline assembly. I tried this:
static inline void __dcc_putchar(char c)
{
unsigned int __c;
asm volatile("uxtb %0, %w1\n"
"msr dbgdtrtx_el0, %0"
: "=r" (__c)
: "r" (c));
isb();
}
it gives this assembly code:
28: 38401423 ldrb w3, [x1],#1
2c: 53001c63 uxtb w3, w3
30: d5130503 msr dbgdtrrx_el0, x3
Is this correct? Shouldn't it be "uxtb x3, w3"?
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
next prev parent reply other threads:[~2015-08-17 23:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-08 0:16 [PATCH 1/3] [v2] hvc_dcc: don't ignore errors during initialization Timur Tabi
2015-08-08 0:16 ` [PATCH 2/3] [v4] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc Timur Tabi
2015-08-10 9:40 ` Will Deacon
2015-08-17 23:56 ` Timur Tabi [this message]
2015-08-18 8:21 ` Dave Martin
2015-08-18 19:07 ` Timur Tabi
2015-08-19 10:14 ` Dave Martin
2015-08-19 16:16 ` Timur Tabi
2015-08-19 16:37 ` Dave Martin
2015-08-24 23:51 ` sboyd at codeaurora.org
2015-09-02 11:10 ` Dave Martin
2015-08-08 0:16 ` [PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC Timur Tabi
2015-08-10 9:47 ` Will Deacon
2015-08-17 22:45 ` Timur Tabi
2015-08-10 9:48 ` [PATCH 1/3] [v2] hvc_dcc: don't ignore errors during initialization Will Deacon
2015-08-19 22:51 ` Timur Tabi
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