linux-kernel - Re: [PATCH 0/2] x86/quark: Add eSRAM driver and test code

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Message-ID: <554A32CB.6070509@nexus-software.ie>
Date:	Wed, 06 May 2015 08:27:07 -0700
From:	Bryan O'Donoghue <pure.logic@...us-software.ie>
To:	Ingo Molnar <mingo2.kernel.org@...il.com>
CC:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, dvhart@...radead.org, andy.schevchenko@...il.com,
	boon.leong.ong@...el.com, linux-kernel@...r.kernel.org,
	platform-driver-x86@...r.kernel.org, derek.browne@...el.com,
	josef.ahmad@...el.com, erik.nyquist@...el.com
Subject: Re: [PATCH 0/2] x86/quark: Add eSRAM driver and test code

On 06/05/15 02:52, Ingo Molnar wrote:
>
> * Bryan O'Donoghue <pure.logic@...us-software.ie> wrote:
>
>> Quark X1000 SoC contains a 512 KiB embedded SRAM (eSRAM) memory that can
>> be mapped onto an area of DRAM in block or on per-page overlay mode where a
>> 4 KiB aligned region can be overlayed - allowing for broken up mappings
>> with a 4 KiB individual granularity.
>>
>> eSRAM has access times similar to an L1 cache. The following patchset
>> adds a gen_pool driver and automatic test routine to exercise eSRAM. The
>> intent of the eSRAM driver is to allow other drivers to allocate SRAM
>> buffers. In contrast to the original BSP code no attempt will be made to
>> map kernel .data section code, this is a simple SRAM buffer allocation/free
>> mechanism and a sanity test to ensure it's ongoing correctness.
>>
>> Bryan O'Donoghue (2):
>>    x86/quark: Add Quark embedded SRAM support
>>    x86/quark: Add Quark embedded SRAM self-test
>
> So I'm wondering what the primary usecase is for this. The eSRAM API
> is purely in-kernel, right? The only user seems to be the self-test.
> What other users will there be?


I see three to four users.

1. UART with DMA enabled.
2. Ethernet/STMMAC
3. SPI/I2C buffers
4. Potentially UIO

I'm working on a good use-case for UIO but rather than patch-bomb eSRAM 
+ other drivers in one go, I thought I'd get the core in and then do 
some modifications in other drivers to utilize the changes.
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