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From: Dave Martin <dave.martin@linaro.org>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>,
	sen wang <wangchendu@gmail.com>,
	David Brown <davidb@codeaurora.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: questions about arm trustzone
Date: Tue, 25 Jan 2011 13:25:02 +0000	[thread overview]
Message-ID: <AANLkTikVW3vcygUQDTH-x6cXkNdf2WEztbTvdz4YkmCk@mail.gmail.com> (raw)
In-Reply-To: <20110125124524.GJ11507@n2100.arm.linux.org.uk>

On Tue, Jan 25, 2011 at 12:45 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote:
>> Avoiding this complexity is one of the motivations for using r7 for
>> the syscall number with CONFIG_EABI (instead of using the SVC comment
>> field).
>
> Your history is not entirely correct.
>
> I had the kernel side of Thumb userspace support in place long before EABI
> came along.  Thumb doesn't have a large enough comment field to store the
> Linux syscall number, so to get around that problem, I decided to use r7
> for the syscall number.  You'll find 2.4 kernels support Thumb instructions
> in userspace.
>
> As part of the EABI switch for ARM mode - which created an incompatible
> SWI interface anyway, we decided that we could reduce data cache pollution
> by eliminating the read of the SWI instruction, so we adopted the r7
> method for ARM EABI mode.
>

Fair enough -- I was glossing over things a bit and I'm not familiar
with all the history.  So, I guess there were plenty of other good
reasons.

Cheers
---Dave

WARNING: multiple messages have this Message-ID (diff)
From: dave.martin@linaro.org (Dave Martin)
To: linux-arm-kernel@lists.infradead.org
Subject: questions about arm trustzone
Date: Tue, 25 Jan 2011 13:25:02 +0000	[thread overview]
Message-ID: <AANLkTikVW3vcygUQDTH-x6cXkNdf2WEztbTvdz4YkmCk@mail.gmail.com> (raw)
In-Reply-To: <20110125124524.GJ11507@n2100.arm.linux.org.uk>

On Tue, Jan 25, 2011 at 12:45 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote:
>> Avoiding this complexity is one of the motivations for using r7 for
>> the syscall number with CONFIG_EABI (instead of using the SVC comment
>> field).
>
> Your history is not entirely correct.
>
> I had the kernel side of Thumb userspace support in place long before EABI
> came along. ?Thumb doesn't have a large enough comment field to store the
> Linux syscall number, so to get around that problem, I decided to use r7
> for the syscall number. ?You'll find 2.4 kernels support Thumb instructions
> in userspace.
>
> As part of the EABI switch for ARM mode - which created an incompatible
> SWI interface anyway, we decided that we could reduce data cache pollution
> by eliminating the read of the SWI instruction, so we adopted the r7
> method for ARM EABI mode.
>

Fair enough -- I was glossing over things a bit and I'm not familiar
with all the history.  So, I guess there were plenty of other good
reasons.

Cheers
---Dave

  reply	other threads:[~2011-01-25 13:25 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-25  2:15 questions about arm trustzone sen wang
2011-01-25  2:15 ` sen wang
2011-01-25  7:49 ` David Brown
2011-01-25  7:49   ` David Brown
2011-01-25  9:19   ` sen wang
2011-01-25  9:19     ` sen wang
2011-01-25 10:26     ` Russell King - ARM Linux
2011-01-25 10:26       ` Russell King - ARM Linux
2011-01-25 11:46       ` Santosh Shilimkar
2011-01-25 11:46         ` Santosh Shilimkar
2011-01-25 12:00         ` Russell King - ARM Linux
2011-01-25 12:00           ` Russell King - ARM Linux
2011-01-25 12:24         ` Dave Martin
2011-01-25 12:24           ` Dave Martin
2011-01-25 12:45           ` Russell King - ARM Linux
2011-01-25 12:45             ` Russell King - ARM Linux
2011-01-25 13:25             ` Dave Martin [this message]
2011-01-25 13:25               ` Dave Martin
2011-03-11 13:02         ` shiraz hashim
2011-03-11 13:02           ` shiraz hashim

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