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Date: Mon, 2 Aug 2010 18:25:23 +0200
Message-ID: <AANLkTikfRja-h9mz7uyRXCZNZjKdU_yB8e58XQucUzrn@mail.gmail.com>
Subject: Re: [PATCH v2 03/20] mmc: support embedded data field in mmc_host
From: Vitaly Wool <vitalywool@gmail.com>
To: Ohad Ben-Cohen <ohad@wizery.com>
Cc: linux-wireless@vger.kernel.org, linux-mmc@vger.kernel.org,
	linux-omap@vger.kernel.org, Kalle Valo <kalle.valo@iki.fi>,
	Pandita Vikram <vikram.pandita@ti.com>, linux@arm.linux.org.uk,
	Nicolas Pitre <nico@fluxnic.net>,
	Tony Lindgren <tony@atomide.com>,
	Roger Quadros <roger.quadros@nokia.com>,
	San Mehat <san@google.com>,
	Chikkature Rajashekar Madhusudhan <madhu.cr@ti.com>,
	Luciano Coelho <luciano.coelho@nokia.com>,
	akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org
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Sender: linux-wireless-owner@vger.kernel.org

Hi Ohad,

On Mon, Aug 2, 2010 at 5:54 PM, Ohad Ben-Cohen <ohad@wizery.com> wrote:

> SPI is using these spi_board_info tables to populate the SPI device
> trees. These tables are registered early at the board-specific init
> code, and are later used by SPI core to populate the devices when the
> SPI master controller is registered.
>
> SDIO doesn't normally needs any kind of hard coded data: most devices
> are dynamically probed and populated.
>
> On rare cases like the wl1271, we have some platform-specific data we
> need to deliver the SDIO function driver (i.e. the irq info in this
> case). Since the device is hardwired to a specific controller, it does
> make some sense to pass this private data from the controller's info
> in the board files, through the host driver, and make it accessible
> through the specific host instance that drives this controller.
>
> Btw, if our problem was be broader (e.g., needs to supply private data
> for non-hardwired devices), then I agree that a more complex
> mechanism, such as the one you suggest, would be needed. But currently
> the problem is very simple and the solution is even simpler: just add
> 1 private pointer to the host.
>
> Hope you find this reasonable,

no, actually I don't. I think this is a hack that intrudes into the
area it completely doesn't belong to.

In fact, one can have 2 views on this problem: either this is a fairly
generic problem we need to address, or this is a very specific corner
case.
Your solution will be treated as a hack in both cases.

If we consider it a generic problem, then we need to find a generic
solution, which is the board_info solution, for instance. FWIW, I2C
also uses this approach now.

If we consider it to be a corner case, let's just add a dummy
platform_device like it's done in WL1251 implementation and keep the
MMC subsystem clean.

Thanks,
   Vitaly