linux-kernel - Re: [PATCH v4 04/10] mtd: pxa3xx_nand: rework flash detection and timing setup

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Date:	Thu, 16 Apr 2015 15:41:34 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	dwmw2@...radead.org, computersforpeace@...il.com
CC:	boris.brezillon@...e-electrons.com, zmxu@...vell.com,
	jszhang@...vell.com, linux-arm-kernel@...ts.infradead.org,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Robert Jarzmik <robert.jarzmik@...e.fr>
Subject: Re: [PATCH v4 04/10] mtd: pxa3xx_nand: rework flash detection and
 timing setup

On 04/16/2015 03:10 PM, Ezequiel Garcia wrote:
> On 04/15/2015 04:11 PM, Sebastian Hesselbarth wrote:
>> On 15.04.2015 19:24, Antoine Tenart wrote:
>>> Rework the pxa3xx_nand driver to allow using functions exported by the
>>> nand framework to detect the flash and to configure the timings.
>>>
>>> Because this driver supports some non-ONFI devices, we also keep the
>>> custom timing setup of this driver so these devices won't break.
>>>
>>> Signed-off-by: Antoine Tenart <antoine.tenart@...e-electrons.com>
>>> ---
>> [...]
>> How about we get rid of the driver specific timings completely
>> and pick up the best onfi timing match instead? The nand_ids table
>> allows for a default_onfi_timing parameter even if onfi itself is
>> not supported.
>>
>> For generic flash, i.e. no specific entry in the nand_ids table,
>> we either choose onfi mode 0 (most conservative) or an even slower
>> one.
>>
>
> I think Robert mentioned [1] that using "ONFI default timings" on
> non-ONFI devices didn't work for him.
>
> [1] https://lkml.org/lkml/2015/3/8/124

Ok, I see. But there is still the option to pass board specific
timings with driver's platform_data. We could use

(a) pdata timings if passed
(b) onfi timings if available
(c) equivalent onfi timings if set
(d) conservative equivalent onfi timings otherwise

All we need is a function to convert sdr_timings to sane driver
timings. And we really need to split this patch into tiny pieces
otherwise it is not reviewable - or at least I need a full overview
about the driver first.

Also, as soon as Robert moves pxa3xx boards fully to DT, we'll loose
the pdata timings option above. *sigh*

Thoughts?

Sebastian
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