linux-kernel - Re: [PATCH v3 04/14] dmaengine: pl330: Add quirk 'arm,pl330-periph-burst'

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Date:   Wed, 15 Jul 2020 11:26:00 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Sugar Zhang <sugar.zhang@...k-chips.com>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        Dan Williams <dan.j.williams@...el.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/14] dmaengine: pl330: Add quirk
 'arm,pl330-periph-burst'

On 29-06-20, 22:05, Sugar Zhang wrote:
> This patch adds the qurik to use burst transfers only
> for pl330 controller, even for request with a length of 1.
> 
> Although, the correct way should be: if the peripheral request
> length is 1, the peripheral should use SINGLE request, and then
> notify the dmac using SINGLE mode by src/dst_maxburst with 1.
> 
> For example, on the Rockchip SoCs, all the peripherals can use
> SINGLE or BURST request by setting GRF registers. it is possible
> that if these peripheral drivers are used only for Rockchip SoCs.
> Unfortunately, it's not, such as dw uart, which is used so widely,
> and we can't set src/dst_maxburst according to the SoCs' specific
> to compatible with all the other SoCs.
> 
> So, for convenience, all the peripherals are set as BURST request
> by default on the Rockchip SoCs. even for request with a length of 1.
> the current pl330 driver will perform SINGLE transfer if the client's
> maxburst is 1, which still should be working according to chapter 2.6.6
> of datasheet which describe how DMAC performs SINGLE transfers for
> a BURST request. Unfortunately, it's broken on the Rockchip SoCs,
> which support only matching transfers, such as BURST transfer for
> BURST request, SINGLE transfer for SINGLE request.
> 
> Finally, we add the quirk to specify pl330 to use burst transfers only.

Applied, thanks

-- 
~Vinod