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From: John Garry <john.garry@huawei.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Brown <broonie@kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	Linuxarm <linuxarm@huawei.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	MTD Maling List <linux-mtd@lists.infradead.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH RFC 1/3] spi: Allow SPI controller override device buswidth
Date: Tue, 3 Mar 2020 09:42:45 +0000	[thread overview]
Message-ID: <f6f21e75-7cee-89da-bb87-95327a4ec2cc@huawei.com> (raw)
In-Reply-To: <CAMuHMdW7Xu6EzfmVFx1+i1byy3KOS5A+h2GuMb8nkZ+-jD1=BA@mail.gmail.com>


Hi Geert,

> 
> On Fri, Feb 28, 2020 at 4:23 PM John Garry <john.garry@huawei.com> wrote:
>> Currently ACPI firmware description for a SPI device does not have any
>> method to describe the data buswidth on the board.
>>
>> So even through the controller and device may support higher modes than
>> standard SPI, it cannot be assumed that the board does - as such, that
>> device is limited to standard SPI in such a circumstance.
>>
>> As a workaround, allow the controller driver supply buswidth override bits,
>> which are used inform the core code that the controller driver knows the
>> buswidth supported on that board for that device.
> 
> Just wondering: can't the controller just override this (e.g. in the .setuup()
> callback) without having to touch the generic code?

I think that this is a good idea.

However, where we call .setup() in spi_setup() looks a little too late - 
at the point we call .setup(), most of the work on vetting/fixing the 
mode bits is complete. And I would not want the SPI controller driver 
just to disregard this work and overwrite the bits (in this way).

And if we wanted to move the .setup callback earlier, then I would be 
worried here with 2 things:
1. Some SPI controller drivers may rely on spi->mode being set finally 
when .setup() is called
2. We may need to undo the work of .setup() if we later error in 
spi_setup(), like for invalid mode bits

However, maybe another callback could be introduced, .early_setup().

Thanks,
John

WARNING: multiple messages have this Message-ID (diff)
From: John Garry <john.garry-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
To: Geert Uytterhoeven <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>
Cc: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	linux-spi <linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Linuxarm <linuxarm-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
	Linux Kernel Mailing List
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	MTD Maling List
	<linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
	Andy Shevchenko
	<andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Subject: Re: [PATCH RFC 1/3] spi: Allow SPI controller override device buswidth
Date: Tue, 3 Mar 2020 09:42:45 +0000	[thread overview]
Message-ID: <f6f21e75-7cee-89da-bb87-95327a4ec2cc@huawei.com> (raw)
In-Reply-To: <CAMuHMdW7Xu6EzfmVFx1+i1byy3KOS5A+h2GuMb8nkZ+-jD1=BA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>


Hi Geert,

> 
> On Fri, Feb 28, 2020 at 4:23 PM John Garry <john.garry-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> wrote:
>> Currently ACPI firmware description for a SPI device does not have any
>> method to describe the data buswidth on the board.
>>
>> So even through the controller and device may support higher modes than
>> standard SPI, it cannot be assumed that the board does - as such, that
>> device is limited to standard SPI in such a circumstance.
>>
>> As a workaround, allow the controller driver supply buswidth override bits,
>> which are used inform the core code that the controller driver knows the
>> buswidth supported on that board for that device.
> 
> Just wondering: can't the controller just override this (e.g. in the .setuup()
> callback) without having to touch the generic code?

I think that this is a good idea.

However, where we call .setup() in spi_setup() looks a little too late - 
at the point we call .setup(), most of the work on vetting/fixing the 
mode bits is complete. And I would not want the SPI controller driver 
just to disregard this work and overwrite the bits (in this way).

And if we wanted to move the .setup callback earlier, then I would be 
worried here with 2 things:
1. Some SPI controller drivers may rely on spi->mode being set finally 
when .setup() is called
2. We may need to undo the work of .setup() if we later error in 
spi_setup(), like for invalid mode bits

However, maybe another callback could be introduced, .early_setup().

Thanks,
John

WARNING: multiple messages have this Message-ID (diff)
From: John Garry <john.garry@huawei.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-spi <linux-spi@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linuxarm <linuxarm@huawei.com>, Mark Brown <broonie@kernel.org>,
	MTD Maling List <linux-mtd@lists.infradead.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH RFC 1/3] spi: Allow SPI controller override device buswidth
Date: Tue, 3 Mar 2020 09:42:45 +0000	[thread overview]
Message-ID: <f6f21e75-7cee-89da-bb87-95327a4ec2cc@huawei.com> (raw)
In-Reply-To: <CAMuHMdW7Xu6EzfmVFx1+i1byy3KOS5A+h2GuMb8nkZ+-jD1=BA@mail.gmail.com>


Hi Geert,

> 
> On Fri, Feb 28, 2020 at 4:23 PM John Garry <john.garry@huawei.com> wrote:
>> Currently ACPI firmware description for a SPI device does not have any
>> method to describe the data buswidth on the board.
>>
>> So even through the controller and device may support higher modes than
>> standard SPI, it cannot be assumed that the board does - as such, that
>> device is limited to standard SPI in such a circumstance.
>>
>> As a workaround, allow the controller driver supply buswidth override bits,
>> which are used inform the core code that the controller driver knows the
>> buswidth supported on that board for that device.
> 
> Just wondering: can't the controller just override this (e.g. in the .setuup()
> callback) without having to touch the generic code?

I think that this is a good idea.

However, where we call .setup() in spi_setup() looks a little too late - 
at the point we call .setup(), most of the work on vetting/fixing the 
mode bits is complete. And I would not want the SPI controller driver 
just to disregard this work and overwrite the bits (in this way).

And if we wanted to move the .setup callback earlier, then I would be 
worried here with 2 things:
1. Some SPI controller drivers may rely on spi->mode being set finally 
when .setup() is called
2. We may need to undo the work of .setup() if we later error in 
spi_setup(), like for invalid mode bits

However, maybe another callback could be introduced, .early_setup().

Thanks,
John

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2020-03-03  9:42 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-28 15:18 [PATCH RFC 0/3] spi/HiSilicon v3xx: Support dual and quad mode through DMI quirks John Garry
2020-02-28 15:18 ` John Garry
2020-02-28 15:18 ` John Garry
2020-02-28 15:18 ` [PATCH RFC 1/3] spi: Allow SPI controller override device buswidth John Garry
2020-02-28 15:18   ` John Garry
2020-02-28 18:25   ` Applied "spi: Allow SPI controller override device buswidth" to the spi tree Mark Brown
2020-02-28 18:25     ` Mark Brown
2020-02-28 18:25     ` Mark Brown
2020-03-01 10:04   ` [PATCH RFC 1/3] spi: Allow SPI controller override device buswidth Sergei Shtylyov
2020-03-01 10:04     ` Sergei Shtylyov
2020-03-01 10:04     ` Sergei Shtylyov
2020-03-02  9:30     ` John Garry
2020-03-02  9:30       ` John Garry
2020-03-02 12:22       ` Mark Brown
2020-03-02 12:22         ` Mark Brown
2020-03-02 12:22         ` Mark Brown
2020-03-02 16:12   ` Geert Uytterhoeven
2020-03-02 16:12     ` Geert Uytterhoeven
2020-03-02 16:33     ` Mark Brown
2020-03-02 16:33       ` Mark Brown
2020-03-02 18:51   ` Geert Uytterhoeven
2020-03-02 18:51     ` Geert Uytterhoeven
2020-03-02 18:51     ` Geert Uytterhoeven
2020-03-03  9:42     ` John Garry [this message]
2020-03-03  9:42       ` John Garry
2020-03-03  9:42       ` John Garry
2020-03-03 12:43       ` Mark Brown
2020-03-03 12:43         ` Mark Brown
2020-03-03 12:43         ` Mark Brown
2020-02-28 15:18 ` [PATCH RFC 2/3] spi: HiSilicon v3xx: Properly set CMD_CONFIG for Dual/Quad modes John Garry
2020-02-28 15:18   ` John Garry
2020-02-28 15:18   ` John Garry
2020-02-28 18:25   ` Applied "spi: HiSilicon v3xx: Properly set CMD_CONFIG for Dual/Quad modes" to the spi tree Mark Brown
2020-02-28 18:25     ` Mark Brown
2020-02-28 18:25     ` Mark Brown
2020-02-28 15:18 ` [PATCH RFC 3/3] spi: HiSilicon v3xx: Use DMI quirk to set controller buswidth override bits John Garry
2020-02-28 15:18   ` John Garry
2020-02-28 16:20   ` Mark Brown
2020-02-28 16:20     ` Mark Brown
2020-02-28 16:20     ` Mark Brown
2020-02-28 17:17     ` John Garry
2020-02-28 17:17       ` John Garry
2020-02-28 17:17       ` John Garry
2020-02-28 18:25   ` Applied "spi: HiSilicon v3xx: Use DMI quirk to set controller buswidth override bits" to the spi tree Mark Brown
2020-02-28 18:25     ` Mark Brown
2020-02-28 18:25     ` Mark Brown

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