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From: "Noralf Trønnes" <noralf@tronnes.org>
To: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: sam@ravnborg.org, david@lechnology.com, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v2 05/11] drm/tinydrm: Remove tinydrm_spi_max_transfer_size()
Date: Tue, 15 Oct 2019 17:41:53 +0200	[thread overview]
Message-ID: <253aec49-e51c-b35b-4e7d-53a8a948655d@tronnes.org> (raw)
In-Reply-To: <20191015143236.GA5363@smile.fi.intel.com>



Den 15.10.2019 16.32, skrev Andy Shevchenko:
> On Fri, Jul 19, 2019 at 05:59:10PM +0200, Noralf Trønnes wrote:
>> spi-bcm2835 can handle >64kB buffers now so there is no need to check
>> ->max_dma_len. The tinydrm_spi_max_transfer_size() max_len argument is
>> not used by any callers, so not needed.
>>
>> Then we have the spi_max module parameter. It was added because
>> staging/fbtft has support for it and there was a report that someone used
>> it to set a small buffer size to avoid popping on a USB soundcard on a
>> Raspberry Pi. In hindsight it shouldn't have been added, I should have
>> waited for it to become a problem first. I don't know it anyone is
>> actually using it, but since tinydrm_spi_transfer() is being moved to
>> mipi-dbi, I'm taking the opportunity to remove it. I'll add it back to
>> mipi-dbi if someone complains.
>>
>> With that out of the way, spi_max_transfer_size() can be used instead.
>>
>> The chosen 16kB buffer size for Type C Option 1 (9-bit) interface is
>> somewhat arbitrary, but a bigger buffer will have a miniscule impact on
>> transfer speed, so it's probably fine.
> 
> This breaks the SPI PXA2xx case I'm using. The world is not a Pi:e.
> 
> [  388.445752] mi0283qt spi-PRP0001:01: DMA disabled for transfer length 153600 greater than 65536
> [  388.634437] mi0283qt spi-PRP0001:01: DMA disabled for transfer length 153600 greater than 65536
> [  388.822933] mi0283qt spi-PRP0001:01: DMA disabled for transfer length 153600 greater than 65536
> 
> The crucial thing is to check the transfer size against maximum DMA length
> of the master.
> 

Isn't this a spi controller driver problem?
spi_max_transfer_size() tells the client what the maximum transfer
length is. The controller driver can use ctlr->max_transfer_size if it
has restrictions.
AFAIUI max_dma_len is used when splitting up the buffer for the sg table
in spi_map_buf().

Noralf.

> Please, fix.
> 
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  parent reply	other threads:[~2019-10-15 15:42 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-19 15:59 [PATCH v2 00/11] drm/tinydrm: Remove tinydrm.ko Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 01/11] drm: Add SPI connector type Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 02/11] drm/tinydrm: Use DRM_MODE_CONNECTOR_SPI Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 03/11] drm/tinydrm: Use spi_is_bpw_supported() Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 04/11] drm/tinydrm: Remove spi debug buffer dumping Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 05/11] drm/tinydrm: Remove tinydrm_spi_max_transfer_size() Noralf Trønnes
2019-10-15 14:32   ` Andy Shevchenko
2019-10-15 15:02     ` Andy Shevchenko
2019-10-15 15:41     ` Noralf Trønnes [this message]
2019-10-15 15:57       ` Daniel Vetter
2019-10-16 16:13         ` Andy Shevchenko
2019-10-16 17:44           ` Daniel Vetter
2019-10-16 18:00             ` Mark Brown
2019-10-17  6:58             ` Andy Shevchenko
2019-10-15 15:59       ` Andy Shevchenko
2019-10-15 16:05         ` Daniel Vetter
2019-10-16  8:07           ` Andy Shevchenko
2019-10-15 16:55         ` Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 06/11] drm/tinydrm: Clean up tinydrm_spi_transfer() Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 07/11] drm/tinydrm: Move tinydrm_spi_transfer() Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 08/11] drm/tinydrm: Move tinydrm_machine_little_endian() Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 09/11] drm/tinydrm/repaper: Don't use tinydrm_display_pipe_init() Noralf Trønnes
2019-07-19 15:59 ` [PATCH v2 10/11] drm/tinydrm/mipi-dbi: Add mipi_dbi_init_with_formats() Noralf Trønnes
2019-07-22 19:48   ` David Lechner
2019-07-19 15:59 ` [PATCH v2 11/11] drm/tinydrm: Move tinydrm_display_pipe_init() to mipi-dbi Noralf Trønnes
2019-07-23 14:11 ` [PATCH v2 00/11] drm/tinydrm: Remove tinydrm.ko Noralf Trønnes

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