linux-kernel - Re: [PATCH v2 3/3] dmaengine: tegra: Add support for dma-channel-mask

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Date:   Fri, 23 Sep 2022 11:50:30 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Akhil R <akhilrajeev@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] dmaengine: tegra: Add support for dma-channel-mask


On 23/09/2022 11:17, Akhil R wrote:
>> On 19/09/2022 12:25, Akhil R wrote:
>>> Add support for dma-channel-mask so that only the specified channels
>>> are used. This helps to reserve some channels for the firmware.
>>>
>>> This was initially achieved by limiting the channel number to 31 in
>>> the driver and adjusting the register address to skip channel0 which
>>> was reserved for a firmware. Now, with this change, the driver can
>>> align more to the actual hardware which has 32 channels.
>>>
>>> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
>>> ---
>>>    drivers/dma/tegra186-gpc-dma.c | 37 +++++++++++++++++++++++++++-------
>>>    1 file changed, 30 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-
>> dma.c
>>> index fa9bda4a2bc6..1d1180db6d4e 100644
>>> --- a/drivers/dma/tegra186-gpc-dma.c
>>> +++ b/drivers/dma/tegra186-gpc-dma.c
>>> @@ -161,7 +161,10 @@
>>>    #define TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT	5000 /* 5
>> msec */
>>>
>>>    /* Channel base address offset from GPCDMA base address */
>>> -#define TEGRA_GPCDMA_CHANNEL_BASE_ADD_OFFSET	0x20000
>>> +#define TEGRA_GPCDMA_CHANNEL_BASE_ADDR_OFFSET	0x10000
>>
>> Why did this value change? There is no mention in the commit message. If
>> this was incorrect before, then this needs to be a separate patch and
>> tagged with the appropriate fixes tag so that this can be picked up for
>> stable.
> This is mentioned in the commit message.
> 
> "... and adjusting the register address to skip channel0 ..."
> 
> Probably it is not very clear that it directs to this change. Shall I update the
> commit message to have a clearer context?

Ah OK. I was wondering how this worked with 'channel_reg_size' but 
looking closer I see channel_reg_size is always SZ_64K. I wonder why we 
even bother having this parameter and don't use SZ_64K directly?

Anyway, for now this is fine.

Jon

-- 
nvpublic