linux-kernel - Re: [PATCH V17 3/6] i2c: tegra: fix maximum transfer size

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Date:   Fri, 8 Feb 2019 21:38:26 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>,
        Shardar Mohammed <smohammed@...dia.com>,
        Timo Alho <talho@...dia.com>
Cc:     "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "peda@...ntia.se" <peda@...ntia.se>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH V17 3/6] i2c: tegra: fix maximum transfer size

08.02.2019 21:37, Sowjanya Komatineni пишет:
>>>>>>  static const struct i2c_adapter_quirks tegra194_i2c_quirks = {
>>>>>>  	.flags = I2C_AQ_NO_ZERO_LEN,
>>>>>> +	.max_write_len = 65535 - I2C_PACKET_HEADER_SIZE,
>>>>>
>>>>> Ideally it should be SZ_64K - I2C_PACKET_HEADER_SIZE to not miss the one byte, otherwise good to me:
>>>>>
>>>>> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
>>>>  
>>>> With SZ_64K - I2C_PACKET_HEADR_Size, When we compute dma_buf_size 
>>>> = max_write_len + I2C_PACKET_HEADER_SIZE, dma_buf_size will be 
>>>> SZ_64K which is 0x10000 apbdma dma count limit should be < 64K 
>>>> meaning 65535 max is allowed
>>>>
>>>
>>> But it's for the GPCDMA, does it have the same 64K limit as APB DMA?
>>
>  64K limit is for APBDMA. This patch has APBDMA support only. No GPCDMA support so buf size limit is based on APBDMA.
>  GPCDMA supports upto 1GB. 
> 
>  I think dma_buf_size is only for buffer allocation so shouldn’t harm for exact 64K.
> Will take a look at dma driver...
> 
> All msg reads, max length is 65535
> All msg writes, max length requests is also limited to 65535 due to u16 type of msg.len So, In any case, we don’t need 65536 bytes.
> Confused, yeah with max write quirk, max transfer can be 64K.
> 
> Will change to 64K instead of 65535.
> 

Good, thank you! Everything else looks good to me.