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    SubjectRe: [PATCH v2 2/6] dt-bindings: dma: dw: Add max burst transaction length property
    On Tue, May 12, 2020 at 12:01:38AM +0300, Andy Shevchenko wrote:
    > On Mon, May 11, 2020 at 11:05:28PM +0300, Serge Semin wrote:
    > > On Fri, May 08, 2020 at 02:12:42PM +0300, Andy Shevchenko wrote:
    > > > On Fri, May 08, 2020 at 01:53:00PM +0300, Serge Semin wrote:
    > > > > This array property is used to indicate the maximum burst transaction
    > > > > length supported by each DMA channel.
    > > >
    > > > > + snps,max-burst-len:
    > > > > + $ref: /schemas/types.yaml#/definitions/uint32-array
    > > > > + description: |
    > > > > + Maximum length of burst transactions supported by hardware.
    > > > > + It's an array property with one cell per channel in units of
    > > > > + CTLx register SRC_TR_WIDTH/DST_TR_WIDTH (data-width) field.
    > > > > + items:
    > > > > + maxItems: 8
    > > > > + items:
    > > >
    > > > > + enum: [4, 8, 16, 32, 64, 128, 256]
    > > >
    > > > Isn't 1 allowed?
    > >
    > > Burst length of 1 unit is supported, but in accordance with Data Book the MAX
    > > burst length is limited to be equal to a value from the set I submitted. So the
    > > max value can be either 4, or 8, or 16 and so on.
    >
    > Hmm... It seems you mistakenly took here DMAH_CHx_MAX_MULT_SIZE pre-silicon
    > configuration parameter instead of runtime as described in Table 26:
    > CTLx.SRC_MSIZE and DEST_MSIZE Decoding.

    No. You misunderstood what I meant. We shouldn't use a runtime parameters values
    here. Why would we? Property "snps,max-burst-len" matches DMAH_CHx_MAX_MULT_SIZE
    config parameter. See a comment to the "SRC_MSIZE" and "DEST_MSIZE" fields of the
    registers. You'll find out that their maximum value is determined by the
    DMAH_CHx_MAX_MULT_SIZE parameter, which must belong to the set [4, 8, 16, 32, 64,
    128, 256]. So no matter how you synthesize the DW DMAC block you'll have at least
    4x max burst length supported.

    -Sergey

    >
    > --
    > With Best Regards,
    > Andy Shevchenko
    >
    >

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