linux-kernel - Re: [PATCH 4/5] ARC: add support for DSP-enabled userspace applications

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Message-ID: <BY5PR12MB403419E2722BE80E329D3409DE390@BY5PR12MB4034.namprd12.prod.outlook.com>
Date:   Thu, 9 Jan 2020 19:01:46 +0000
From:   Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexey Brodkin" <Alexey.Brodkin@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
Subject: Re: [PATCH 4/5] ARC: add support for DSP-enabled userspace
 applications

Hi Vineet,

>From: Vineet Gupta <vgupta@...opsys.com>
>On 12/27/19 10:03 AM, Eugeniy Paltsev wrote:
>> To be able to run DSP-enabled userspace applications we need to
>> save and restore following DSP-related registers:
>> At IRQ/exception entry/exit:
>>  * ACC0_GLO, ACC0_GHI, DSP_CTRL
>>  * ACC0_LO, ACC0_HI (we already save them as r58, r59 pair)
>> At context switch:
>>  * DSP_BFLY0, DSP_FFT_CTRL
[snip]
>> +
>> +#ifndef __ASSEMBLY__
>> +
>> +/* some defines to simplify config sanitize in kernel/setup.c */
>> +#if defined(CONFIG_ARC_DSP_KERNEL)    || \
>> +    defined(CONFIG_ARC_DSP_USERSPACE)
>> +#define ARC_DSP_HANDLED                      1
>> +#else
>> +#define ARC_DSP_HANDLED                      0
>> +#endif
>
>This is a really bad idea - u r introducing explicit include dependencies which
>can change even outside of arch changes !
>We've dealt with enough of these problems with current.h, so best to avoid, even
>if there is some code clutter.

Hmm, would it be OK if I add this option as a private kconfig option?
I.E (for ARC_DSP_HANDLED):

---------------->8----------------------
config ARC_DSP_HANDLED
	def_bool n

choice
	prompt "DSP support"
	default ARC_DSP_NONE
	help
	  Depending on the configuration, CPU can contain DSP registers
	  (ACC0_GLO, ACC0_GHI, DSP_BFLY0, DSP_CTRL, DSP_FFT_CTRL).
	  Bellow is options describing how to handle these registers in
	  interrupt entry / exit and in context switch.

config ARC_DSP_NONE
	bool "No DSP extension presence in HW"
	help
	  No DSP extension presence in HW

config ARC_DSP_KERNEL
	bool "DSP extension in HW, no support for userspace"
	select ARC_HAS_ACCL_REGS
	select ARC_DSP_HANDLED
	help
	  DSP extension presence in HW, no support for DSP-enabled userspace
	  applications. We don't save / restore DSP registers and only do
	  some minimal preparations so userspace won't be able to break kernel

config ARC_DSP_USERSPACE
	bool "Support DSP for userspace apps"
	select ARC_HAS_ACCL_REGS
	select ARC_DSP_HANDLED
	help
	  DSP extension presence in HW, support save / restore DSP registers to
	  run DSP-enabled userspace applications
endchoice
---------------->8----------------------

---
 Eugeniy Paltsev