From: Santosh Shilimkar <santosh.shilimkar@ti.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robherring2@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Russell King <linux@arm.linux.org.uk>,
Olof Johansson <olof@lixom.net>,
Grant Likely <grant.likely@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Linus Walleij <linus.walleij@linaro.org>,
"Strashko, Grygorii" <grygorii.strashko@ti.com>
Subject: Re: [PATCH v3 4/7] of: configure the platform device dma parameters
Date: Tue, 6 May 2014 16:44:40 -0400 [thread overview]
Message-ID: <536949B8.3030106@ti.com> (raw)
In-Reply-To: <7182186.5Q53eQg77F@wuerfel>
On Tuesday 06 May 2014 05:40 AM, Arnd Bergmann wrote:
> On Monday 05 May 2014 17:47:32 Santosh Shilimkar wrote:
>
>> + dev->coherent_dma_mask = DMA_BIT_MASK(32);
>> + if (!dev->dma_mask)
>> + dev->dma_mask = &dev->coherent_dma_mask;
>> +
>> + /*
>> + * if dma-ranges property doesn't exist - just return else
>> + * setup the dma offset
>> + */
>> + ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>> + if (ret < 0) {
>> + dev_dbg(dev, "no dma range information to setup\n");
>> + return;
>> + }
>> +
>> + /* DMA ranges found. Calculate and set dma_pfn_offset */
>> + dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
>> + dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
>> +}
>
> I think there should at least be a comment about why we are computing
> the correct DMA mask here and then ignore that and just use DMA_BIT_MASK(32)
> instead. I understand that Russell and Rob prefer it that way and I'm not
> going to argue, but I find it counterintuitive and I think it deserves
> an explanation in the source code for anybody who is trying to figure
> out how things fit together.
>
In this patch, the dma_mask related code is just moved. We are not calculating
dma_mask either. I was looking for the history of how DMA_BIT_MASK(32)
landed up but couldn't trace it down apart from the fact that the code was
carried from powerPC. May be Rob knows.
How about below comment ? I didn't delibratly added point about bus
intercepting drivers dma_set_*mask() call etc.
/*
* Set default dma-mask to 32 bit. Drivers are expected to setup
* the correct supported dma_mask.
*/
+ dev->coherent_dma_mask = DMA_BIT_MASK(32);
+ if (!dev->dma_mask)
+ dev->dma_mask = &dev->coherent_dma_mask;
Regards,
Santosh
next prev parent reply other threads:[~2014-05-06 20:45 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-24 15:30 [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 1/7] device: introduce per device dma_pfn_offset Santosh Shilimkar
2014-05-02 1:01 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 2/7] of: introduce of_dma_get_range() helper Santosh Shilimkar
2014-05-02 1:06 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 3/7] of: introduce of_dma_is_coherent() helper Santosh Shilimkar
2014-05-02 0:56 ` Rob Herring
2014-05-05 21:45 ` Santosh Shilimkar
2014-05-05 22:06 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 4/7] of: configure the platform device dma parameters Santosh Shilimkar
2014-04-29 14:41 ` Grant Likely
2014-04-30 14:19 ` Santosh Shilimkar
2014-05-01 13:12 ` Grant Likely
2014-05-01 13:16 ` Santosh Shilimkar
2014-05-02 9:58 ` Arnd Bergmann
2014-05-02 13:13 ` Santosh Shilimkar
2014-05-02 15:13 ` Arnd Bergmann
2014-05-27 12:56 ` Grant Likely
2014-05-27 13:30 ` Arnd Bergmann
2014-05-28 8:23 ` Linus Walleij
2014-05-28 13:29 ` Arnd Bergmann
2014-05-28 13:32 ` Linus Walleij
2014-05-28 14:04 ` Santosh Shilimkar
2014-05-29 14:01 ` Linus Walleij
2014-05-29 14:08 ` Santosh Shilimkar
2014-05-29 19:24 ` Arnd Bergmann
2014-05-29 20:04 ` Santosh Shilimkar
2014-05-02 0:49 ` Rob Herring
2014-05-05 21:47 ` Santosh Shilimkar
2014-05-05 22:08 ` Rob Herring
2014-05-06 9:40 ` Arnd Bergmann
2014-05-06 20:44 ` Santosh Shilimkar [this message]
2014-05-07 13:24 ` Santosh Shilimkar
2014-05-02 16:54 ` Bjorn Helgaas
2014-05-02 18:59 ` Arnd Bergmann
2014-05-05 20:45 ` Bjorn Helgaas
2014-05-05 20:55 ` Arnd Bergmann
2014-05-05 22:28 ` Bjorn Helgaas
2014-05-06 3:44 ` Benjamin Herrenschmidt
2014-05-06 9:54 ` Arnd Bergmann
2014-05-06 13:32 ` Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 5/7] ARM: dma: Use dma_pfn_offset for dma address translation Santosh Shilimkar
2014-05-02 14:32 ` Rob Herring
2014-05-02 14:58 ` Russell King - ARM Linux
2014-05-02 15:05 ` Santosh Shilimkar
2014-05-05 19:50 ` Russell King - ARM Linux
2014-05-05 21:43 ` Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 6/7] ARM: dma: implement set_arch_dma_coherent_ops() Santosh Shilimkar
2014-05-02 0:58 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 7/7] ARM: dma: use phys_addr_t in __dma_page_[cpu_to_dev/dev_to_cpu] Santosh Shilimkar
2014-04-24 15:45 ` Will Deacon
2014-05-01 13:19 ` [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent Santosh Shilimkar
2014-05-01 13:25 ` Russell King - ARM Linux
2014-05-01 14:06 ` Santosh Shilimkar
2014-05-02 14:41 ` Rob Herring
2014-05-02 16:41 ` Santosh Shilimkar
2014-05-14 10:12 ` Grant Likely
2014-06-02 6:37 ` Shawn Guo
2014-06-02 13:24 ` Santosh Shilimkar
2014-06-02 15:06 ` Arnd Bergmann
2014-06-02 15:54 ` Santosh Shilimkar
2014-06-02 19:00 ` Arnd Bergmann
2014-06-02 19:08 ` Santosh Shilimkar
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