lkml.org 
[lkml]   [2018]   [Jul]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 05/14] dmaengine: dma-jz4780: Add support for the JZ4740 SoC
    On Tue, Jul 17, 2018 at 9:34 AM Vinod <vkoul@kernel.org> wrote:
    >
    > On 16-07-18, 15:33, Rob Herring wrote:
    > > On Mon, Jul 09, 2018 at 10:42:26PM +0530, Vinod wrote:
    > > > On 03-07-18, 14:32, Paul Cercueil wrote:
    > > >
    > > > > enum jz_version {
    > > > > + ID_JZ4740,
    > > > > ID_JZ4770,
    > > > > ID_JZ4780,
    > > > > };
    > > > > @@ -247,6 +248,7 @@ static void jz4780_dma_desc_free(struct virt_dma_desc *vdesc)
    > > > > }
    > > > >
    > > > > static const unsigned int jz4780_dma_ord_max[] = {
    > > > > + [ID_JZ4740] = 5,
    > > > > [ID_JZ4770] = 6,
    > > > > [ID_JZ4780] = 7,
    > > > > };
    > > > > @@ -801,11 +803,13 @@ static struct dma_chan *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
    > > > > }
    > > > >
    > > > > static const unsigned int jz4780_dma_nb_channels[] = {
    > > > > + [ID_JZ4740] = 6,
    > > > > [ID_JZ4770] = 6,
    > > > > [ID_JZ4780] = 32,
    > > > > };
    > > >
    > > > I feel these should be done away with if we describe hardware in DT
    > >
    > > The compatible property can imply things like this.
    >
    > So what is the general recommendation, let DT describe hardware
    > including version delta or use compatible to code that in driver?

    Compatible is the version. Looking at the above, the version or ID
    isn't even stable.

    > Is it documented anywhere?

    Not really. It's a judgment call generally. Maybe # of DMA channels
    should be a property because that is something most controllers have.
    But you really have to define the property up front, not when the 2nd
    version of h/w shows up with different properties.

    To start defining guidelines, a couple of things come to mind:

    - Define properties for parameters that vary from board to board (for one SoC).
    - You can't add new required properties to existing bindings, so the
    not present default must work for all existing compatibles (or you
    need per compatible driver data).
    - Bugs/quirks/errata should be handled by compatible, not adding a
    property. Because bugs should be fixable without a dtb update and only
    a kernel update.

    Rob

    \
     
     \ /
      Last update: 2018-07-17 19:41    [W:2.996 / U:1.120 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site